Saving & investing
Compound Interest Calculator
See how savings grow with compound interest. Add monthly or yearly deposits, choose the compounding frequency and get a year-by-year table and APY.
Balance after 20 years
$79,306.13
$34,000.00 paid in · $45,306.13 earned
Total deposits
$24,000.00
$100.00 a month, $1,200.00 a year, plus $10,000.00 to start
Interest earned
$45,306.13
57% of the final balance
Effective annual rate (APY)
6.168%
6% nominal, monthly
Why 6% a year earns 6.168%
6% is the nominal rate: the headline figure, before compounding. It is credited 12 times a year at r = 0.5% a time, and each credit earns interest for the rest of the year, so a full year actually returns (1 + r)^12 − 1 = 6.168%.
That effective figure, the APY, is the one to compare between accounts. Two nominal rates only mean the same thing when they are credited on the same schedule, which is why 6% compounded monthly and 6% compounded yearly are different products.
Why the deposit timing is worth $231.02
Your $100.00 deposits land at the end of each month, after that month's interest has been credited, so each one only starts earning from the next. Moving them to the start of the period gives every deposit one extra month of growth and ends at $79,537.15, $231.02 more.
Before tax and inflation. An estimate, not financial advice, providers may calculate differently.
- Starting amount
- Deposits
- Interest
How the balance grows
| Year | Deposits | Interest | End balance |
|---|
The projection steps a month at a time at the effective monthly rate, so the month rows are the calculation itself and each year row is twelve of them added up.
A result link includes the numbers you entered. Share it only with people you want to see them.
How this is calculated
Interest that is credited to an account starts earning interest itself, so each period's growth is calculated on a slightly larger balance than the last, and over years the small differences stack into a curve that bends upward. The calculator takes a starting amount, an optional regular deposit, the interest rate, how often interest is credited and the number of years, projects the balance month by month, and reports the final figure, how much of it you paid in, how much is interest, and the effective annual rate (APY) the compounding schedule produces. When the deposit and compounding schedules match, the projection reproduces the closed-form formula exactly.
FVP × (1 + r)n + c × ((1 + r)n − 1) ÷ r
- FV
- the final balance
- P
- the starting amount
- c
- the deposit made at the end of every period
- r
- the rate per period: the annual rate divided by the periods a year
- n
- the total number of periods: years × periods a year
What this does not include
- Tax on interest, which in an ordinary account is charged every year.
- Inflation: the final balance is in nominal money, not today's.
- Rate changes: the rate you enter is held for the whole term.
- Account or fund fees; enter the rate net of them.
How this calculator works
Compound interest explained: the formula, APY and a 20-year example. The future-value formula behind the projection, how deposit timing and daily compounding are handled, why APY is the figure to compare, and two worked ledgers.
This calculator is for general information only and is not financial advice. Results are estimates based on the figures you enter and the stated formula; lenders and providers may round or calculate differently. Check any decision with the institution involved or a qualified adviser.