A 3-year-old leopard gecko is about 20 in human years; a veiled chameleon of the same age is about 47
There is no official chart for converting a lizard's age into human years. We could not find one in veterinary references or in animal hospital guides, and lizard species differ too much in how fast they grow and age for a single chart to work. A veiled chameleon reaches sexual maturity at 4 to 5 months and Old World chameleons live 3 to 8 years in captivity, while crested geckos and Argentine tegus live 15 to 20 years. So instead of one formula, this calculator uses documented life milestones for each species and matches each to the same point in a human life. Sexual maturity is matched to human puberty (the mean age at first period among US women is 12.5), the midpoint of the typical captive lifespan to human life expectancy (79.0 years for babies born in the US in 2024), and the points in between are joined with straight lines. For a species with a recorded lifespan longer than its typical lifespan range, that longest record is matched to the longest human lifespan on record, 122 years 164 days.
By this method a 3-year-old leopard gecko is about 20 in human years and fully grown, while a veiled chameleon of the same age is about 47 and a little over a year from the senior stage. Pick a species in the calculator above and enter an age or a hatch date to see the human age, the life stage and the time left until the end of the typical lifespan range. The species lanes below put all 15 species on one 0 to 30 year axis, so you can see where the same age falls in each life. If you don't know the species, choose “Don't know (compare species)” to see the lowest and highest values.
When a human-age estimate is useful
Lizards grow far faster than people, and species differ several-fold in how quickly they age. A plain number of years hides some turning points, and translating them into human years makes a few decisions easier.
- Thinking about breeding: breeding before a female is mature is hard on her. PetMD advises not breeding a female bearded dragon until she is at least 2 years old, because younger animals can run into complications while laying eggs. A 1-year-old bearded dragon is about 8 in human years, which makes the reason to wait easy to see.
- Deciding whether to adopt: crested geckos, uromastyx and Argentine tegus typically live 15 to 20 years. A gecko adopted by a elementary-school child can live until that child is an adult. Even leopard geckos live 10 to 15 years according to VCA Animal Hospitals, and more than 20 years according to the Merck Veterinary Manual.
- Caring for an older lizard: in this calculator the senior stage begins at a human age of about 57 to 62, whatever the species. That is 9 years 5 months for a leopard gecko, 5 years 8 months for a bearded dragon and 4 years 2 months for a veiled chameleon. The Royal Veterinary College (RVC) animal hospital recommends a health check every year for leopard and crested geckos; once your lizard is a senior, it helps to log changes in weight and appetite more often so you have something to show at the check-up.
- Bringing home a lizard of unknown species: at the same 3 years, the human age ranges from about 11 (Nile monitor) to about 47 (veiled chameleon). You have to identify the species before the age means anything.
How the calculation works
- Anchor points per species: (the midpoint of the sexual-maturity range, human 12.5) and (the midpoint of the typical captive lifespan range, human 79.0), plus hatching at (0, 0). The 7 species whose longest record is longer than the end of the typical lifespan range add (the longest recorded lifespan, human 122 years 164 days). For a leopard gecko that is 1 year 9 months, the midpoint of 18 to 24 months (San Diego Zoo); 12.5 years, the midpoint of 10 to 15 years (VCA); and 28.5 years, the longest record in the AnAge database.
- Straight lines between points: between sexual maturity and the lifespan midpoint, human age = 12.5 + (lizard months − 21) ÷ (150 − 21) × (79.0 − 12.5). A 3-year-old (36 months) leopard gecko gives 12.5 + 15 ÷ 129 × 66.5 = 20.2, which rounds to 20.
- Past the lifespan midpoint: for the 7 species with a record, the calculator switches to a gentler line from that point (79.0) to the longest record (122.4). A leopard gecko older than 12.5 years gains about 2.7 human years per year. The 8 species without such a record (crested gecko, African fat-tailed gecko, uromastyx, veiled and panther chameleons, ackie monitor, Nile monitor and Argentine tegu) simply continue on the slope of the previous segment. When the human age passes 122 years 164 days, the longest human lifespan on record, the calculator shows “122+” instead of a number, and it stops one year after the longest record (or after the end of the typical lifespan range when there is no record).
- Life stages: juvenile (hatching until maturity begins), maturing (the sexual-maturity range), adult, senior and long-lived. We found no veterinary standard for when a lizard becomes a senior, so the calculator borrows the American Animal Hospital Association (AAHA) guideline for dogs, which counts the last 25% of the expected lifespan as the senior stage. Here that means the senior stage starts at 75% of the lifespan midpoint. Long-lived means past the lifespan midpoint, the age that matches human life expectancy.
- Entering a hatch or adoption date: the age is counted in whole months up to today, plus the fraction of the current month that has passed. With an adoption date, the calculator goes back by the age at adoption (in months) to estimate a hatch date, using the last day of the month when the same day does not exist.
- Order of sources: for typical lifespan we used the range in the Merck Veterinary Manual table “Average Life Span of Reptiles in Captivity” when it has one, then VCA Animal Hospitals, LafeberVet, PetMD, RSPCA, zoos and museums, and finally Animal Diversity Web. Sexual maturity follows the same order. When a source gives a single value such as “about 15 years”, that value is used as is.
Human age by lizard age
Human ages for five popular species. The word in parentheses is the life stage at that age, and a dash means the age is more than one year past that species' longest recorded lifespan, where the calculator stops.
| Lizard age | Leopard gecko | Crested gecko | Bearded dragon | Blue-tongued skink | Veiled chameleon |
|---|---|---|---|---|---|
| 6 months | 4 (juvenile) | 8 (maturing) | 4 (juvenile) | 2 (juvenile) | 14 (adult) |
| 1 year | 7 (juvenile) | 13 (adult) | 8 (maturing) | 4 (juvenile) | 21 (adult) |
| 2 years | 14 (adult) | 17 (adult) | 18 (adult) | 8 (juvenile) | 34 (adult) |
| 3 years | 20 (adult) | 21 (adult) | 29 (adult) | 13 (adult) | 47 (adult) |
| 5 years | 33 (adult) | 29 (adult) | 51 (adult) | 24 (adult) | 73 (senior) |
| 7 years | 45 (adult) | 37 (adult) | 73 (senior) | 35 (adult) | 98 (long-lived) |
| 10 years | 64 (senior) | 49 (adult) | 89 (long-lived) | 51 (adult) | — |
| 15 years | 86 (long-lived) | 69 (senior) | 108 (long-lived) | 79 (long-lived) | — |
| 20 years | 99 (long-lived) | 89 (long-lived) | — | 98 (long-lived) | — |
Reading across a row shows how much species matter. At 2 years a blue-tongued skink is a juvenile of about 8 in human years, while a veiled chameleon is a 34-year-old adult. Crested geckos reach adult size early, so they read older than leopard geckos at ages 1 to 3, but their typical lifespan of 15 to 20 years is longer, and from age 5 they come out younger.
Anchor points and sources by species
Reference values for the 15 species in the calculator. We included only species for which the age at maturity and the typical captive lifespan could be confirmed in veterinary sources, animal hospitals, zoos, museums or university databases. Gargoyle geckos, leachianus geckos (New Caledonian giant geckos), day geckos and savannah monitors, which were in the previous version, were dropped because we could not find a source for their age at sexual maturity or typical lifespan.
| Species | Sexual maturity | Typical lifespan | Longest record | Senior from |
|---|---|---|---|---|
| Leopard gecko | 18–24 months (San Diego Zoo) | 10–15 years (VCA) | 28.5 years (AnAge) | 9 years 5 months |
| Crested gecko | Adult size at 6–12 months (PetMD)* | 15–20 years (PetMD) | None | 13 years 2 months |
| African fat-tailed gecko | 8–11 months (ADW) | 10–20 years (ADW) | None (ADW: up to about 20 years) | 11 years 3 months |
| Tokay gecko | About 1 year (Smithsonian) | About 10 years (Smithsonian) | 23.5 years (AnAge) | 7 years 6 months |
| Bearded dragon | 1–2 years (ADW) | 5–10 years (Merck) | 18 years 237 days (Guinness) | 5 years 8 months |
| Chinese water dragon | 2–3 years (LafeberVet) | 12–15 years (LafeberVet) | 15.3 years (AnAge) | 10 years 2 months |
| Uromastyx | 18–24 months (LafeberVet) | About 15–20 years (LafeberVet) | None | 13 years 2 months |
| Green iguana | By 2 years (VCA) | 5–15 years (Merck) | 25 years (reported by VCA) | 7 years 6 months |
| Veiled chameleon | 4–5 months (ADW) | 3–8 years (Merck, Old World chameleons) | None (ADW: males up to 8 years) | 4 years 2 months |
| Panther chameleon | 6–9 months (LafeberVet) | 3–8 years (Merck, Old World chameleons) | None | 4 years 2 months |
| Jackson's chameleon | 6–9 months (LafeberVet) | 3–8 years (Merck, Old World chameleons) | 8.2 years (AnAge) | 4 years 2 months |
| Blue-tongued skink | Adult at about 3 years (Australian Museum)* | About 15 years (Smithsonian) | 26.6 years (AnAge) | 11 years 3 months |
| Ackie monitor | About 1 year (Smithsonian) | 10–15 years (Smithsonian) | None | 9 years 5 months |
| Nile monitor | 3–4 years (ADW) | 10–20 years (ADW) | None (AnAge: 14.6 years) | 11 years 3 months |
| Argentine tegu | Around 3 years (Potter Park Zoo) | 15–20 years (Potawatomi Zoo) | None | 13 years 2 months |
Values in the table were checked against the original sources on October 23, 2026. * We found no source for the age of sexual maturity in crested geckos and blue-tongued skinks, so the age at which they reach adult size (PetMD: 6–12 months; Australian Museum: about 3 years, total length about 400 mm) is used instead. A longest record is used only when it is longer than the end of the typical lifespan range; “None” marks the 8 species whose maximum age in the sources falls within the typical range or that have no record at all.
How long lizards live: why the sources disagree
Even for the same species, lifespans differ quite a bit between sources. Typical lifespan depends on housing and care, while the longest record is the single oldest animal, usually in a zoo. The table below collects the popular species by source; the value in bold is the one this calculator uses.
| Species | Veterinary and animal hospital sources | Other sources |
|---|---|---|
| Leopard gecko | Merck over 20 years · VCA 10–15 years · PetMD up to 10–20 years | RSPCA and RVC up to 20 years · ADW about 22 years · AnAge longest 28.5 years |
| Crested gecko | PetMD 15–20 years · RVC 15–20 years | RSPCA up to 15–20 years |
| Bearded dragon | Merck 5–10 years · VCA 7–12 years · PetMD 8–10 years | RSPCA 10–15 years or more · Guinness longest 18 years 237 days |
| Green iguana | Merck 5–15 years · VCA 10–15 years (25 years reported) · PetMD over 15 years | ADW over 20 years in captivity · AnAge longest 19.8 years |
| Chameleons | Merck Old World chameleons 3–8 years · LafeberVet panther 2–5 years, Jackson's 3–8 years or more · PetMD veiled over 5 years | ADW veiled females typically 5 years, males up to 8 · San Diego Zoo over 10 years with specialist care |
The Merck Veterinary Manual says only “over 20 years” for the leopard gecko, with no range, so we used the next source in line, VCA's 10 to 15 years. Some animals live longer, as Merck's “over 20 years” and RSPCA's “up to 20 years” show, and the calculator labels those as long-lived.
What to watch for at each life stage
Juvenile and maturing
The juvenile stage runs from hatching until sexual maturity begins, and the maturing stage covers the sexual-maturity range. Growth is fast, so feeding is frequent. The RSPCA says to feed baby leopard geckos every day and adults every other day, while VCA suggests once a day or every other day for young leopard geckos and two to three times a week for adults. Breeding behavior can begin during the maturing stage, so reconsider whether males and females should share an enclosure.
Adult
This is the longest stage, from the end of maturity to the start of the senior stage: for a leopard gecko from 2 years to 9 years 5 months, for a bearded dragon from 2 years to 5 years 8 months. Once a lizard is fully grown, check that the enclosure still fits its size. The RVC animal hospital recommends a health check every year.
Senior and long-lived
The senior stage starts at a human age of about 57 to 62, and the long-lived stage begins once the lizard passes the midpoint of its typical lifespan, which corresponds to human life expectancy. At these ages, keeping a steady record of weight, appetite, shedding and droppings makes small changes easy to notice. If a lizard suddenly loses weight or refuses food, don't put it down to age; take it to a veterinarian who treats reptiles.
Common mistakes
- A fixed multiplier such as “1 lizard year = n human years”: growth rate and lifespan differ by species, so no single multiplier works. Across the 15 species here, a 1-year-old lizard ranges from about 4 to 21 in human years. The previous version of this calculator also used a formula proportional to average lifespan and an unsourced split into stages; we could not verify them and replaced them.
- Reading the longest record as the normal lifespan: 28.5 years for a leopard gecko is the longest record in the AnAge database, while the typical lifespan VCA gives is 10 to 15 years. Reading age against the record makes an animal look younger than it is.
- Entering the adoption date as the hatch date: many lizards are already several months old when you get them. Use the adoption date and enter the age at adoption in months.
- Treating all chameleons as one species: the veiled chameleon matures at 4 to 5 months (ADW), but San Diego Zoo gives 1 to 2 years for chameleon maturity depending on the species. The sexes also differ: a female veiled chameleon typically lives 5 years and a male up to 8 (ADW).
- Judging age by size alone: San Diego Zoo says leopard geckos mature at a weight of a little over 30 g, and PetMD says a crested gecko reaches adult size in 6 to 12 months “with proper care”. Size depends on husbandry, so a hatch date or breeder's record is more reliable when you have one.
Limitations
- The result is an estimate that joins documented anchor points with straight lines, not a conversion set by any veterinary body. There is no evidence that aging proceeds evenly between the anchor points.
- Typical lifespan differs between sources, and the calculator picked one by source priority. Using another source can change the human age by anything from a few years to more than ten.
- For the crested gecko and the blue-tongued skink we used the age of reaching adult size in place of sexual maturity, and for the tokay gecko, blue-tongued skink and green iguana some anchor points are single values, not ranges.
- The 8 species with no record longer than their typical lifespan range are less accurate, because the human age past the lifespan midpoint is the previous slope extended. For the Chinese water dragon (record 15.3 years) and Jackson's chameleon (8.2 years), whose record is almost the same as the end of the range, the human age climbs quickly toward 120 near the end of the range.
- The senior-stage rule is borrowed from the AAHA guideline for dogs (the last 25%), not from any lizard source.
- The human anchor points use US figures: life expectancy at birth of 79.0 years (2024, both sexes) and a mean age at first period of 12.5 years, reported by women aged 15–44 surveyed in 2013–2017. The median in that survey was 11.9; the calculator uses the mean. Because the menarche figure comes from women only, it serves only as a rough marker for puberty.
- This calculator does not assess health. If your lizard refuses food, has trouble shedding or moves differently, contact a veterinarian who treats reptiles. In the US you can look one up through the Association of Reptilian and Amphibian Veterinarians (ARAV). What you enter is calculated in this browser only and is never sent to a server.
Sources
- 01MSD/Merck Veterinary Manual — Selecting a ReptileTable “Average Life Span of Reptiles in Captivity”: bearded dragon 5–10 years, green iguana 5–15 years, leopard gecko over 20 years, Old World chameleons 3–8 years (revised 2026-06)
- 02VCA Animal Hospitals — Leopard Geckos: Care and Feeding · Iguanas: Owning · Bearded Dragons: OwningLeopard gecko 10–15 years; young animals fed once a day or every other day, adults 2–3 times a week / Iguana sexually mature by 2 years, 10–15 years, 25 years reported / Bearded dragon 7–12 years
- 03PetMD — Crested Gecko Care Sheet · Bearded Dragon Care Sheet · Leopard Gecko Care SheetCrested gecko adult size at 6–12 months, 15–20 years (2025-11) / Bearded dragon 8–10 years, do not breed females before at least 2 years (2026-07) / Leopard gecko up to 10–20 years, adult at 1–2 years (2026-05)
- 04LafeberVet — Basic Information for Uromastyx · Chinese or Green Water Dragons · Panther Chameleon · Jackson's ChameleonUromastyx 18–24 months, about 15–20 years / Water dragon sexually mature at 2–3 years when over 40 cm long, 12–15 years / Chameleons mature at 6–9 months, panther 2–5 years, Jackson's 3–8 years or more
- 05RSPCA — Leopard gecko · Crested gecko · Bearded dragonLeopard gecko up to 20 years, babies fed daily, adults every other day / Crested gecko up to 15–20 years in captivity / Bearded dragon typically 10–15 years or more
- 06Royal Veterinary College — Leopard gecko care · Crested gecko careLeopard gecko up to 20 years in captivity, crested gecko 15–20 years, yearly health check (reviewed 2024-12)
- 07San Diego Zoo Wildlife Alliance — Leopard gecko · ChameleonLeopard gecko weighs a little over 30 g, sexually mature at about 18–24 months / Chameleon maturity 1–2 years depending on species, over 10 years with specialist care
- 08Smithsonian's National Zoo — Tokay gecko · Spiny-tailed monitor · Northern blue-tongued skink · Asian water dragonTokay mature at about 1 year, live about 10 years / Ackie (spiny-tailed) monitor mature at about 1 year, 10–15 years / Blue-tongued skink about 15 years / Water dragon 10–15 years
- 09Australian Museum — Eastern Blue-tongue · Potter Park Zoo · Potawatomi Zoo — Argentine Black and White TeguBlue-tongue adult at about 3 years, several animals reached 20 years in captivity / Tegu sexually mature at around 3 years, 15–20 years
- 10Animal Diversity Web (University of Michigan) — Chamaeleo calyptratus · Hemitheconyx caudicinctus · Varanus niloticusBearded dragon mature at 1–2 years / Veiled chameleon mature at 4–5 months, females typically 5 years, males up to 8 / Fat-tailed gecko mature at 8–11 months, typically 10–20 years in captivity (over 15, up to about 20) / Nile monitor mature at 3–4 years, 10–20 years in captivity
- 11AnAge (Human Ageing Genomic Resources) databaseMaximum longevity in captivity: leopard gecko 28.5 years, tokay gecko 23.5, blue-tongued skink 26.6, green iguana 19.8, water dragon 15.3, Jackson's chameleon 8.2
- 12Guinness World Records — Oldest bearded dragon ever · Oldest person everBearded dragon Sebastian 18 years 237 days (died 2016-01-24) / Jeanne Louise Calment 122 years 164 days
- 13AAHA — 2019 Canine Life Stage GuidelinesSenior: the last 25% of estimated lifespan until the end of life (for dogs; borrowed here as the senior-stage rule)
- 14CDC National Center for Health Statistics — Mortality in the United States, 2024 (NCHS Data Brief No. 548)Life expectancy at birth 79.0 years in 2024 (males 76.5, females 81.4), published January 2026 — checked 2026-10-11
- 15CDC National Center for Health Statistics — Trends and Patterns in Menarche in the United States: 1995 through 2013–2017 (National Health Statistics Reports No. 146)Mean age at menarche 12.5 years and median 11.9 years among women aged 15–44, National Survey of Family Growth 2013–2017, published Sep 10, 2020 — checked 2026-10-11
Frequently asked questions
How old is a 1-year-old leopard gecko in human years?
About 7 with this calculator, still in the juvenile stage. Leopard geckos reach sexual maturity at about 18 to 24 months, when they weigh a little over 30 g (San Diego Zoo). The calculator matches the midpoint, 1 year 9 months, to the human age at puberty of 12.5, and the midpoint of the typical lifespan of 10 to 15 years (VCA Animal Hospitals), 12.5 years, to the US life expectancy of 79.0. A 2-year-old is about 14, a 3-year-old about 20 and a 5-year-old about 33, and the senior stage starts at 9 years 5 months.
How old is a crested gecko in human years?
A 1-year-old is about 13, a 3-year-old about 21, a 5-year-old about 29 and a 10-year-old about 49. We found no veterinary or zoo source for the age of sexual maturity in crested geckos, so the calculator uses the midpoint of the 6 to 12 months PetMD gives for reaching adult size, 9 months, as the age of puberty. The typical lifespan is 15 to 20 years (PetMD, RSPCA), so they age more slowly than other geckos, and the senior stage starts at 13 years 2 months.
How many human years is one lizard year?
It depends on the species, so no single number works. Across the 15 species in this calculator, a 1-year-old lizard ranges from about 4 in human years (Nile monitor) to about 21 (veiled chameleon). Veiled chameleons, which mature at 4 to 5 months (panther and Jackson's at 6 to 9), grow fast, while Nile monitors, which mature at 3 to 4 years, grow slowly. If you don't know the species, choose "Don't know" in the species list to see the lowest and highest values.
How long do bearded dragons live?
It depends on the source. The Merck Veterinary Manual gives 5 to 10 years, VCA Animal Hospitals 7 to 12, PetMD 8 to 10 and the RSPCA 10 to 15 years or more, and the Guinness record is 18 years 237 days. This calculator uses Merck's 5 to 10 years, matches the midpoint of 7.5 years to the US life expectancy of 79.0 and starts the senior stage at 5 years 8 months. A 3-year-old is about 29 and a 5-year-old about 51.
Why do chameleons gain human years so fast?
They live a short time and mature early. The Merck Veterinary Manual gives 3 to 8 years for Old World chameleons in captivity, and the veiled chameleon matures at 4 to 5 months (Animal Diversity Web). A 1-year-old veiled chameleon is therefore about 21 in human years, a 3-year-old about 47, and the senior stage starts at 4 years 2 months. The same source says female veiled chameleons typically live 5 years and males up to 8.
What if I don't know my lizard's hatch date?
Choose the adoption date and enter the age at adoption in months; the calculator goes back by that many months from the adoption date to estimate a hatch date. The most accurate age at adoption is in the records of the breeder or shop you got the animal from. If you only know the rough age, the age input works too. If you enter the adoption date as the hatch date, the animal will look younger by its age at adoption.
Why do sources give different lifespans for lizards?
Sources look at different animals and use different standards. Typical lifespan depends on housing and care, while the longest record is the single oldest animal, often in a zoo. For example, leopard geckos live 10 to 15 years according to VCA and up to 10 to 20 years according to PetMD, while the longest record in the AnAge database is 28.5 years. The calculator picks one typical lifespan by source priority and lists the other values in the table in the text.
At what age is a lizard a senior?
We found no veterinary standard for when a lizard becomes a senior. The calculator borrows the AAHA guideline for dogs, which counts the last 25% of the expected lifespan as the senior stage, and starts the senior stage at 75% of the midpoint of the typical lifespan. That is 9 years 5 months for a leopard gecko, 5 years 8 months for a bearded dragon and 4 years 2 months for a veiled chameleon, and for all 15 species it corresponds to a human age of about 57 to 62.