$10,000 at 1% a month for 12 months grows to $11,268.25
This calculator takes a starting amount and assumes the same return repeats every day, month or year. It then shows the balance at the end. Put $10,000 at 1% a month for 12 months and you end with $11,268.25, a profit of $1,268.25 and a total return of 12.68%. With simple interest, where the 1% is only ever paid on the original $10,000, you would have $11,200.00, so compounding adds $68.25. Stretch the same plan to 120 months and compounding gives $33,003.87 against $22,000.00 for simple interest, a gap of $11,003.87.
It is built for a single lump sum with no further deposits. If you add money every month, use the compound interest calculator with monthly contributions instead. Below you will find when this kind of calculation helps, how it works, how compound differs from simple interest, how to turn a monthly or daily return into a yearly one, how long it takes to double your money, what 1% a day really means, and where the numbers stop being reliable.
When this calculation is useful
The calculator answers one question: if x% happens every period, n times in a row, what is the result? That fits a savings or investing target such as 0.5% a month, where you want to see what the target is worth if it were always met. It fits the opposite case too, such as a trading habit that loses 0.5% a day, where you want to see how far the balance falls. You can type a growth rate instead of a return. Revenue that grows 5% a month, a newsletter that adds 3% more subscribers each month or prices that rise with inflation all follow the same formula.
Inflation is a good everyday example. If prices rise 3% a year, something that costs $100 today costs about $134.39 in ten years. A common slip is to say "1% a month is 12% a year". With compounding it is 12.68%, and the annualized row in the results shows that figure, so you can also use it to compare products that quote different period lengths on the same one-year basis.
How it is calculated
- Enter the starting amount. It is a single deposit, with nothing added later.
- Choose the period length (day, month or year) and how many periods to run. The limits are 3,650 days, 600 months or 100 years.
- Enter the return that repeats each period, as a percentage. For a loss, enter a negative number above −100%.
- Optionally open the extra fields to change the start date or add an exchange rate. The start date defaults to today and sets the dates in the table and for the doubling point. The exchange rate adds the result in euros.
- The projected amount appears in large type. A bar shows the split between principal and profit, and the rows below show total return, annualized return, the simple-interest result and when the money doubles. The chart draws the compound curve against the straight simple-interest line, and hovering shows the amount for each period.
The formula is projected amount = starting amount × (1 + return per period)number of periods. For $10,000, 1% a month and 12 months, that is 10,000 × 1.0112 = $11,268.25. The Consumer Financial Protection Bureau describes compounding as earning interest "on the money you've saved and on the interest you earn along the way". The exponent in the formula is that process. The calculator uses the power directly rather than multiplying period by period, and it rounds the displayed amounts to the cent.
Simple versus compound interest
Simple interest multiplies only the starting amount by the rate, so the same dollar amount is added every period. Compound interest multiplies the whole balance, profit included, so the amount added grows each period. Over a short stretch the two are close. Over a long one the gap widens quickly.
| Scenario | Simple | Compound | Difference |
|---|---|---|---|
| $10,000 · 1%/month · 12 months | $11,200.00 | $11,268.25 | $68.25 |
| $10,000 · 1%/month · 36 months | $13,600.00 | $14,307.69 | $707.69 |
| $10,000 · 1%/month · 120 months | $22,000.00 | $33,003.87 | $11,003.87 |
| $10,000 · 0.1%/day · 365 days | $13,650.00 | $14,402.51 | $752.51 |
| $100,000 · 5%/year · 10 years | $150,000.00 | $162,889.46 | $12,889.46 |
| $100,000 · 5%/year · 30 years | $250,000.00 | $432,194.24 | $182,194.24 |
At 5% a year, compounding beats simple interest by 8.6% after 10 years and by 73% after 30. The "With simple interest" row and the dashed line on the chart show the same comparison for whatever you enter.
Turning a monthly or daily return into a yearly one
Multiplying a period return by the number of periods gives a simple-interest figure, which is not what compounding delivers. For the compound one-year figure use (1 + return per period)periods in a year − 1, with 12 periods for months and 365 for days. This is also why a bank advertises an APY next to its plain rate. FINRA explains that "the APY is larger than the basic, or nominal, rate since it takes into account the impact of compounding".
| Return per period | Simple multiplication | Compound, per year |
|---|---|---|
| 1% a month | 12% | 12.68% |
| 0.5% a month | 6% | 6.17% |
| 2% a month | 24% | 26.82% |
| 0.1% a day | 36.5% | 44.03% |
| 0.05% a day | 18.25% | 20.02% |
| 1% a day | 365% | 3,678.34% |
With small returns the two figures are close. With 1% a day, the compound result is about ten times the simple one. The annualized row appears automatically whenever the period is a day or a month.
When your money doubles
Dividing 72 by the return per period, in percent, gives a rough count of periods to double. This is the Rule of 72, and the SEC's Investor.gov teaching materials cover it alongside compound interest. The exact answer is log 2 ÷ log(1 + return). The calculator finds the first period where the balance reaches twice the start and shows it, with its date, in the "When it doubles" row and as a ×2 marker on the chart.
| Return per period | Rule of 72 estimate | Actual first period past double |
|---|---|---|
| 1% a month | 72 months | month 70 |
| 2% a month | 36 months | month 36 |
| 0.5% a month | 144 months | month 139 |
| 0.1% a day | 720 days | day 694 |
| 5% a year | 14.4 years | year 15 |
| 7% a year | 10.3 years | year 11 |
| 10% a year | 7.2 years | year 8 |
The rule is a shortcut and is least exact at the extremes. For a loss, the same slot shows when the balance falls to half. A loss of 1% a day halves your money on day 69.
What 1% a day for 365 days means
1.01 raised to the 365th power is about 37.78, so $10,000 growing 1% a day for a year becomes $377,834.34. Lose 1% a day instead and 0.99365 is about 0.0255, which leaves $255.18. The huge gap makes this a popular line about small daily habits. As an investment return it is not realistic, because 1% every day is 3,678.34% a year. Use the "$10,000 · 1%/day · 365 days" preset to see the shape of compounding, and use something like 0.1% a day or 1% a month for planning.
Common mistakes
- Typing a yearly return into the monthly setting. Entering 12% with the period set to months means 12% every month, which multiplies your money by almost 3.9 in a year. Switch the period to year, or convert the yearly return first.
- Dividing a yearly return by 12 to get a monthly one. A 12% yearly return compounded monthly is about 0.9489% a month, not 1%. Entering 1% a month gives 12.68% for the year, a little more than 12%.
- Quoting a period return times the number of periods as a yearly return. 1% a month is 12.68% compounded, not 12%. 0.1% a day is 44.03%, not 36.5%.
- Treating the result as money in hand. Taxes and fees are not subtracted. Interest and investment gains can be taxable, and trading and fund costs reduce what you keep.
- Assuming a past average repeats exactly. Real returns differ from period to period and some periods lose money. Two paths with the same average can end in different places.
Limits of this calculator
- The return is assumed to be identical every period. Extra deposits, withdrawals and changing returns are not modeled.
- Taxes, fees and inflation are not calculated. For those, and for monthly contributions, see the compound interest calculator with monthly contributions.
- Monthly and yearly dates land on the same day of the month as the start date, and a month without that day uses its last day (January 31 plus one month is February 28). Daily periods add one calendar day each.
- The euro conversion divides the result by the rate you enter, in dollars per euro. It does not forecast exchange rates.
- Results above $1 quadrillion are not calculated, and amounts are shown rounded to the cent.
Reference date The definition of compound interest and the APY wording were checked against the sources below on 2026-10-15. The numbers in the tables are results of this calculator. Returns such as 1% a month, 0.1% a day or 5% a year are examples, not forecasts.
Sources
- 01CFPB: How does compound interest work?Compound interest is earned on the money you have saved and on the interest you earn along the way
- 02FINRA: Bank ProductsEarnings are added to the balance to create a larger base, and the APY is larger than the nominal rate because of compounding
- 03U.S. SEC Investor.gov: What is compound interest?How compounding works and the Rule of 72
Frequently asked questions
How much is $10,000 at 1% a month for 12 months?
It becomes $11,268.25. The 1% is added 12 times, so the math is 10,000 × 1.01^12. Profit is $1,268.25, a total return of 12.68%. With simple interest you would have $11,200.00, so compounding adds $68.25.
Is 1% a month the same as 12% a year?
No. Twelve months of 1% compound to 12.68% for the year, because each month's gain earns its own gain. The annualized return row of this calculator shows that figure. Going the other way, a 12% yearly return is about 0.9489% a month, not 1%.
Does 1% a day for a year really multiply money by 37?
In the math, yes. 1.01^365 is about 37.78, so $10,000 becomes $377,834.34. Losing 1% a day gives 0.99^365, about 0.0255, and leaves $255.18. No real investment repeats the same daily return for 365 days, so treat it only as a picture of compounding.
How long does it take to double money at 1% a month?
The Rule of 72 gives 72 ÷ 1 = 72 months as an estimate. The exact answer is month 70. At 0.1% a day it is day 694 (estimate 720), and at 5% a year it is year 15 (estimate 14.4). The calculator shows the exact period and date.
What is the difference between simple and compound interest for $10,000 at 1% a month over 120 months?
Simple interest gives $22,000.00 because the same $100 is added every month. Compound interest gives $33,003.87 because each month's 1% applies to a growing balance. The difference is $11,003.87.
Can I enter a negative return?
Yes. Any number above −100% works as a loss scenario, and the row "When it halves" shows the period where the balance drops to half. At −1% a day that is day 69.
Are taxes and fees included in the final amount?
No. The calculator assumes the entered return repeats unchanged every period. Subtract taxes, trading or fund fees and inflation yourself, or use the compound interest calculator with monthly contributions, which has tax and inflation fields.
What does the exchange rate field do?
Enter dollars per euro, for example 1.08, and the projected amount and profit are also shown in euros. The result in dollars is divided by that rate, and no future exchange-rate change is predicted.