Compound Interest Calculator

Model a savings balance

1. Enter a starting amount, a nominal annual percentage and 1–100 whole years. Use the same currency for every amount; this tool does not convert currencies or choose a market rate.
2. Choose Monthly or Yearly. That interval controls both compounding and regular deposits, so enter the amount added each month or each year. Choose whether those deposits arrive at the beginning or end of each period.
3. Read the ending balance together with total contributed, interest and the assumptions. Open the yearly table for the path through time; allow separately for fees, taxes, inflation and changing rates.

Understand the model before using the number

A nominal annual rate is divided by the number of compounding periods per year. For example, 12% means 1% per month in Monthly mode, not a 12% effective annual yield, APY or AER. With one yearly compounding period, the nominal and effective annual percentages coincide numerically in this model.

The starting amount is present at time zero. Regular deposits are separate: Monthly makes 12 deposits per year and Yearly makes one. Beginning-period deposits earn one more period of interest than the corresponding end-period deposits; neither option adds an extra deposit.

Total contributed includes the starting amount and every regular deposit. Interest growth is the remaining part of the balance, not another deposit. The calculation retains fractional interest internally and rounds only the displayed year-end and final amounts to 0.01; it does not round each interest credit like an account might.

Monthly and yearly deposits keep separate drafts so changing intervals never silently reinterprets an amount. The same rate, term and total cash added can still produce different growth when deposit timing or compounding frequency changes.

Examples with explicit timing

With 1000 initially, 100 at each month-end, a 5% nominal annual rate and 10 years, the model gives about 17175.24. Of that, 13000.00 was contributed and 4175.24 is displayed interest. The 5% is an illustration, not an expected or recommended return.

With 1000 initially, 100 at each year-end, 10% and two years, the ending balance is 1420.00. Moving those same two deposits to the beginning of each year gives 1441.00; the starting amount and deposit count have not changed.

At a zero rate, 1000 initially plus 100 each month for 10 years gives 13000.00 and no interest, regardless of deposit timing. A tiny positive rate is different: when positive interest rounds below one hundredth, the result says less than 0.01 rather than claiming no growth.

An illustrative model, not an account forecast

The rate and deposit amount stay constant. Taxes, fees, inflation, losses, withdrawals, changing rates, actual calendar days and product-specific accrual or crediting are not modeled. An effective annual yield cannot simply be substituted for a nominal rate when compounding monthly. This is not personal financial advice or a guarantee of future performance.

This version supports monthly or yearly compounding with matching deposit intervals, whole-year terms and balances up to 1000000000 currency units before rounding. It does not predict exchange rates or enforce each currency's settlement rules. Two-decimal results describe the display model, not the purchasing power or certainty of the amount.

In-page calculation

Calculations use your entries in the browser without uploading them or adding saved history or input-bearing links. Copy is optional. Existing site services still apply; this is not a certification of third-party services.