Compound interest calculator
Compound interest applies the rate to the balance, then to the balance plus the interest already added. A contribution can be added at the beginning or at the end of each compounding period.
The rate you enter is a nominal annual rate. It is split evenly across the compounding periods. Amounts in the table are rounded to the nearest hundredth. This is an illustration, not a forecast of an investment.
Calculator
Required fields are marked with *.
Use a comma or a dot for the decimal, as in 12.5 or 12,5. Type thousands as 1000 or 1 000. A single comma or dot is the decimal mark, so 1,000 means 1.
Results
The result will appear here.
How to use this calculator
- Enter the starting amount, the annual rate, and the number of years.
- Choose how often the rate is applied. Add a contribution of zero if there is none.
- Choose whether each contribution arrives before or after that period’s interest.
Formula
For a rate of zero, the ending balance is the start plus every contribution. No interest is added.
Otherwise each period multiplies the current balance by 1 plus the periodic rate. A contribution at the beginning is included before that multiplication. A contribution at the end is added after it.
periodic rate = annual rate / periods per year
With no contributions, that repetition matches the closed form below. P is the start, r is the periodic rate, and N is the number of periods.
future value = P × (1 + r)^N
Worked example
1,000 at 10 percent, compounded once a year, for 2 years
After the first year the balance is 1,000 × 1.10 = 1,100.
After the second year it is 1,100 × 1.10 = 1,210. Interest earned is 210. If the rate were zero and you added 50 at the end of each month for a year, the balance would be 1,000 + 600 = 1,600.
The balance is 1,210. Interest is 210.
Questions
What is the difference between beginning and end?
A contribution at the beginning earns interest in that same period. A contribution at the end does not earn interest until the next period. With a zero rate the timing does not change the total.
Does the table include the original amount as a contribution?
No. The “contributed this year” column lists only the periodic contributions. The starting amount is included in “total contributed” in the summary.
Can this price a real savings account?
No. Banks may use a different day count, fees, or a rate that changes. The page also ignores taxes.
Sources
Last reviewed November 1, 2026