Compound interest calculator
Starting money
Rate and time
Balance over time
Principal and contributions are shown separately from estimated interest.
Annual schedule
Rows show each full year, with the final row shortened when months are included.
| Year | Starting balance | Interest | Ending balance |
|---|---|---|---|
| 1 | $10,000 | $581 | $13,581 |
| 2 | $13,581 | $765 | $17,346 |
| 3 | $17,346 | $957 | $21,303 |
| 4 | $21,303 | $1,160 | $25,463 |
| 5 | $25,463 | $1,372 | $29,835 |
| 6 | $29,835 | $1,596 | $34,431 |
| 7 | $34,431 | $1,831 | $39,263 |
| 8 | $39,263 | $2,078 | $44,341 |
| 9 | $44,341 | $2,338 | $49,679 |
| 10 | $49,679 | $2,611 | $55,291 |
Formula and methodology
Nominal annual rates are compounded at the selected frequency. APY inputs are first converted to an equivalent nominal annual rate for that same frequency. Continuous compounding uses exponential growth.
Assumptions
Contributions are evenly spaced. Beginning contributions are added at the start of each contribution period, including time zero; end contributions are added at the end of each period.
No advice or live rates
This educational calculator uses only the assumptions you enter. It does not use live rates, connect to accounts, include taxes, fees, inflation, or provide personalized financial advice.
FAQ and help
Use nominal annual rate when you know the stated rate before compounding. Use the APY toggle when your bank, savings account, or example already gives an annual percentage yield.
Why timing matters
Beginning-period contributions have more time to earn interest than end-period contributions. The difference grows with larger deposits, higher rates, and longer time horizons.
Need help?
See the compound interest calculator help page for inputs, methodology, FAQ, and troubleshooting.
Related calculators
Compare this topic with the APY , Investment , Retirement pages.
How compound interest grows a balance
Compound interest means each period's interest is added to the balance, so later periods earn interest on the interest already credited. Over short horizons the effect is small; over decades it can become the largest part of a balance. The calculator above shows that split directly: the chart separates what you contributed from what compounding added.
The compounding formula in plain terms
A nominal annual rate is divided by the number of compounding periods per year, then applied once per period. $10,000 at a 6% nominal rate compounded monthly grows by 0.5% twelve times a year, which is slightly more than 6% annually because each month builds on the last. Continuous compounding takes the same idea to its mathematical limit using exponential growth.
Why compounding frequency matters
The same nominal rate produces different yearly growth depending on how often it compounds. A 5% nominal rate yields exactly 5% with annual compounding, about 5.12% with monthly compounding, and about 5.13% with daily compounding. The gaps look small but accumulate over long horizons. The APY calculator converts between nominal rates and effective annual yields for each frequency.
A worked example
$10,000 at a 5% nominal annual rate compounded monthly grows to about $16,470 after 10 years with no further deposits — roughly $6,470 of interest. Add $100 at the end of each month and the balance reaches about $32,000: $22,000 contributed in total and about $10,000 earned. Contributions do most of the work early on, while compounding does more of it the longer the money stays invested, a pattern the investment calculator and retirement calculator extend to multi-decade plans.
The Rule of 72 shortcut
To estimate doubling time, divide 72 by the annual rate. At 6%, money doubles in roughly 12 years; at 9%, in roughly 8. It is an approximation that works best for rates in the single digits, but it is a quick sanity check on any compound growth projection before you trust the detailed numbers. For a longer walkthrough with more worked examples, read How Compound Interest Works.