The next dose time is the last dose time plus the minimum interval
If a label says “every 4 to 6 hours” and you took the medicine at 9:00 a.m., the earliest next dose is the short end of the range added to that time: 1:00 p.m. If the label also gives a daily limit, such as “do not exceed 6 tablets in 24 hours,” there is a second check. What you took in the last 24 hours plus the dose you are about to take must stay under the limit. If you are already at the limit, you wait until your oldest dose is more than 24 hours old.
The calculator above runs both checks for each medicine. Every card in the medicine box shows the earliest time you can take it again and how long is left, and the ring fills as that time gets closer. A dose logged earlier than the interval is marked “Early dose,” and the daily timeline shows when you took each dose, the stretches when the next dose is not yet allowed, and your sleep hours.
Why intervals matter and when this calculator helps
Spacing doses by the label interval and staying under the 24-hour maximum are the two things a label asks of you. The FDA states that the maximum total amount of acetaminophen taken in 24 hours should not be more than 4,000 mg for adults and children 12 years of age and older. The DailyMed label for 200 mg ibuprofen tablets says to take 1 tablet every 4 to 6 hours while symptoms persist and not to exceed 6 tablets in 24 hours unless directed by a doctor. Both numbers are easy to lose track of after a few doses.
A written record is more reliable than memory in situations like these.
- Taking a pain reliever or fever reducer several times in a day: it is easy to forget what time the last dose was, and where the “24 hours” starts.
- Taking cold medicine, an antibiotic and a supplement together: each has its own interval, so it is hard to see which one is due next.
- Sharing care of a child or a parent: send the same log by link or file so two people do not give the same dose twice.
- Waking up at night and wondering if you can take another dose: mark your sleep hours on the daily timeline and doses that fall overnight show up in advance.
How to use the calculator
- Add a medicine: tap “Add medicine” in the medicine box and type a name. The color only helps you tell medicines apart on the timeline.
- Minimum interval: enter the interval from the label or prescription in hours and minutes. If the label gives a range such as “every 4 to 6 hours,” the short end is the minimum interval.
- Dose and 24-hour maximum (optional): if the label has a daily limit, enter the dose and the limit. If the limit is a number of doses, choose “doses” as the maximum unit.
- Log a dose: if you just took it, tap “I took it.” If you took it at another time, enter the date, time and amount under Dose log in the settings. Delete a wrong entry with the × button.
- Read the result: the top shows the time until the nearest next dose, the medicine box shows the state of each medicine, and below are the daily timeline and the order of the next 24 hours.
Nothing is saved on your device at first. To keep your list, turn on “Save on this device.” To move it to another device, use “Save to file” and “Load file.” A link made with “Copy link” keeps the medicine names and the last 3 days of records only after the # in the address, so they are not sent to a server.
How it is calculated
- The 24-hour window: for any time T, the “last 24 hours” runs up to T and leaves out anything exactly 24 hours before T. A dose taken exactly 24 hours ago drops out of the window.
- When you hit the maximum: if the total would go over, the time is pushed back to when the oldest dose in the window ages past 24 hours, and the total is checked again.
- The next dose amount: the calculation uses the dose set in the settings. If you plan to take less this time, change the dose first.
- Early doses: a dose logged before the next possible time worked out from the earlier records. The next time is counted again from that dose.
- Time units: records are stored rounded down to the minute, and intervals are counted in real elapsed time.
Reading the results from sample inputs
These are the next possible times the calculator gives for the same inputs on October 19, 2026. Times use the 24-hour clock.
| Inputs | Doses logged | Next possible time | Why |
|---|---|---|---|
| 4-hour interval | 09:00 | 13:00 (1:00 p.m.) | Last dose + 4 hours |
| 4-hour interval, 2 tablets per dose, 24-hour max 8 tablets | 01:00, 05:00, 09:00, 13:00 (2 tablets each) | Next day 01:00 | At 17:00 the 24-hour total is 8 tablets, so one more dose would make 10. Wait until the 01:00 dose drops out. |
| 8-hour interval, 2 tablets per dose, 24-hour max 6 tablets | 07:00, 15:00, 23:00 (2 tablets each) | Next day 07:00 | The 07:00 dose is exactly 24 hours old and drops out, so the total is 4 + 2 = 6 tablets. |
| 4-hour interval, 24-hour max 5 doses | 06:00, 10:00, 14:00, 18:00, 22:00 | Next day 06:00 | At 02:00 it would be dose 6. Wait until the 06:00 dose drops out. |
| 6-hour interval | 08:00, 12:00 | 18:00 (6:00 p.m.) | The 12:00 dose came before 14:00, so it is an “Early dose.” The 6 hours count from it. |
| 8-hour interval, now 16:00 | 07:00 | Now (from 15:00, 3:00 p.m.) | The scheduled time passed an hour ago. See the missed dose section. |
Entering label and prescription wording
“3 times a day” and “every 8 hours” are not the same instruction, so they go into the calculator differently. “Every 8 hours” is a minimum interval. “3 times a day” is a limit on the number of doses in 24 hours, which you enter as a maximum in doses.
| Label or prescription wording | Minimum interval | 24-hour maximum |
|---|---|---|
| Every 4 to 6 hours | 4 hours | Also enter the label’s daily maximum |
| Every 8 hours / every 12 hours | 8 hours / 12 hours | Enter it if the label gives one |
| Maximum of N tablets per day | The label’s interval | N tablets |
| Do not exceed N tablets in 24 hours | The label’s interval | N tablets |
| Maximum of N doses per day | The label’s interval | N doses (unit “doses”) |
| Take with meals | Follow the prescription. If no interval was given, ask your doctor or pharmacist. | Leave blank (meal times shift from day to day, so a 24-hour count can flag a breakfast dose as early) |
If a prescription says to take a medicine with meals, take it as prescribed. Enter an interval only when your doctor or pharmacist gave you one.
Numbers on two common pain reliever labels
These are the adult directions in the sources below. The same ingredient can have different directions by product, strength and age, and labels change, so read the label on the medicine you have first.
| Product (ingredient) | Dose and interval | Daily limit |
|---|---|---|
| Ibuprofen tablets, 200 mg (OTC label on DailyMed) | Adults and children 12 years and older: 1 tablet every 4 to 6 hours while symptoms persist | Do not exceed 6 tablets in 24 hours, unless directed by a doctor |
| Acetaminophen (FDA) | Follow the label of your product | No more than 4,000 mg in 24 hours for adults and children 12 years and older |
The sources checked for this page give no per-dose amount or interval for acetaminophen, so none is listed here. Enter the interval from your own label.
When alternating two fever reducers
If a doctor told you to alternate two fever reducers, enter the two medicines separately. The calculator keeps each medicine to its own interval and daily maximum, but it does not calculate the gap between two different medicines. Check the gap your doctor set by looking at the dose records of both medicines on the daily timeline.
If you miss a dose
MedlinePlus says about ibuprofen: if you are taking it on a regular basis, take the missed dose as soon as you remember it. However, if it is almost time for the next dose, skip the missed dose and continue your regular dosing schedule. Do not take a double dose to make up for a missed one. For other medicines, check the label or ask a pharmacist, because the rule differs by medicine.
When the interval has passed, the calculator changes the medicine to “OK to take now” and shows how long ago the scheduled time passed. It does not quietly push a missed dose to a later time, so you can see how late you are and decide whether to skip it.
When different products contain the same ingredient
The FDA limit of 4,000 mg is stated as the maximum total amount of acetaminophen taken in 24 hours, so every product that contains acetaminophen counts toward it. A cold medicine and a pain reliever with different names can contain the same ingredient. Check the active ingredients on each label.
In the calculator, it is more accurate to put products with the same ingredient on one line. Enter the dose in mg and the 24-hour maximum in mg. Then the total is counted in one place even when you switch between products with different tablet strengths.
Common mistakes
- Pushing the next time back automatically when the interval passes: the missed dose disappears from the screen. This calculator counts only from your last real record.
- Counting “maximum per day” from midnight: doses at 11 p.m. and 1 a.m. fall on different dates but are 2 hours apart. This calculator counts the last 24 hours.
- Entering “every 4 to 6 hours” as 6 hours: it is not wrong, but it tells you a later time. Enter the short end to see the earliest time.
- Taking a different amount and leaving the record unchanged: if you took 1 tablet, log 1, or the 24-hour total will be wrong.
- Using the same interval for extended-release and regular tablets: the interval and the limit can differ by product.
- Reading “3 times a day” as every 8 hours: when a medicine is taken with meals, follow the prescription.
Limits and cautions
- The calculator only works out times from the interval and limit you enter. It does not judge doses, interactions or contraindications from a medicine name.
- It does not calculate doses based on weight, such as children’s fever reducers. Follow the product label or the amount your doctor or pharmacist gave you.
- It does not send reminders. Open the page to see the next time.
- Records stay in this browser only when “Save on this device” is on. Clearing browser data erases them.
- If you took more than directed, call Poison Help at 1-800-222-1222 right away, and call 911 in an emergency.
As of The sources below were checked on 2026-10-19.
Sources
- 01U.S. FDA. Acetaminophen (August 14, 2025)Maximum total of 4,000 mg in 24 hours for adults and children 12 years and older
- 02DailyMed. Ibuprofen tablet, 200 mg, OTC label (February 26, 2025)1 tablet every 4 to 6 hours, no more than 6 tablets in 24 hours unless directed by a doctor
- 03MedlinePlus. IbuprofenWhat to do about a missed dose, and not taking a double dose
- 04HRSA Poison Help. About usThe Poison Help line, 1-800-222-1222, connects you to your local poison center
Frequently asked questions
How many hours until I can take the next dose?
From the last dose time plus the minimum interval on the label or prescription. If the label says every 4 to 6 hours, the short end, 4 hours, is the minimum interval, so a dose at 9:00 a.m. can be repeated from 1:00 p.m. For a medicine with a daily limit, the amount taken in the last 24 hours must be checked too.
How often can I take ibuprofen 200 mg tablets?
The DailyMed OTC label for 200 mg ibuprofen tablets says adults and children 12 years and older should take 1 tablet every 4 to 6 hours while symptoms persist, and not exceed 6 tablets in 24 hours unless directed by a doctor. Your product may differ, so check its label.
What is the daily limit for acetaminophen?
The FDA says the maximum total amount of acetaminophen taken in 24 hours should not be more than 4,000 mg for adults and children 12 years of age and older. Because it is a total, every product that contains acetaminophen counts toward it.
Is the 24-hour maximum counted from midnight?
No. This calculator counts the last 24 hours, not the calendar day. Doses at 11 p.m. and 1 a.m. are on different dates but only 2 hours apart. If the last 24 hours plus one dose would go over the maximum, the next time is pushed back until the oldest dose is more than 24 hours old.
Is “3 times a day” the same as every 8 hours?
Not necessarily. “Every 8 hours” is a minimum interval between doses. If a prescription says to take a medicine with meals, follow the prescription. Enter an interval only for medicines you were told to take every so many hours, and leave the 24-hour maximum blank for meal-timed medicines, because meal times shift from day to day.
What should I do if I miss a dose?
MedlinePlus says about ibuprofen: if you take it on a regular basis, take the missed dose as soon as you remember it, but if it is almost time for the next dose, skip the missed dose and continue your regular schedule. Do not take a double dose to make up for a missed one. For other medicines, check the label or ask a pharmacist.
Can I alternate two fever reducers?
If a doctor told you to alternate them, enter the two medicines separately. The calculator keeps each medicine to its own interval and daily maximum, but it does not calculate the gap between two different medicines. Check the gap your doctor set on the daily timeline.
Where are my records stored?
Nowhere at first. If you turn on “Save on this device,” they stay in this browser only, and turning it off deletes them. To move them, use “Save to file” and “Load file,” or “Copy link,” which keeps names and the last 3 days of records only after the # in the address, so they are not sent to a server.