SmartCost Lab

Compound Savings Calculator

Project how a savings balance grows with regular monthly deposits, any compounding frequency and rising contributions — and, if you like, what it will be worth in today's money after inflation.

Last reviewed 16 October 2026 · How we build and check calculators

$

Example value.

$

Example value.

%

Required. Use the rate your bank or fund quotes. We don't pre-fill a rate because savings rates change often and differ by account.

Optional

%
%

Leave blank to skip. Our Inflation calculator shows each country's recent official CPI history if you want a reference point.

Results will appear here

Fill in the highlighted fields. Anything marked as required has no verified default, so we need your own figure.

Why we ask you for the interest rate

Savings rates differ enormously between accounts — from close to nothing on some current and checking accounts to much higher rates on fixed-term deposits or promotional offers — and they change whenever central banks move. A default would be wrong for most people, so the rate field starts empty. Enter the rate your bank quotes, and use the scenario tabs to compare two accounts.

Nominal rate, AER and APY

Banks often quote a nominal annual rate plus a compounding frequency, and an effective annual rate that includes the compounding: AER in the UK, APY in the US. If you only know the AER/APY, enter it with yearly compounding and the result will be the same. The calculator shows the effective rate for whatever you enter:

effective annual rate = (1 + r ÷ n)ⁿ − 1 e.g. 5% compounded monthly → (1 + 0.05/12)¹² − 1 = 5.116%

How the projection is calculated

The balance is simulated month by month. Each month the balance grows by the equivalent monthly rate and your deposit is added at the start or end of the month:

monthly rate = (1 + r ÷ n)^(n ÷ 12) − 1 balance(next month) = balance × (1 + monthly rate) + deposit today's money = balance ÷ (1 + inflation)^years

Converting the compounding frequency to an equivalent monthly rate means deposits made during the year earn interest pro rata. Some accounts credit interest only once a year and pay nothing on money deposited mid-year; for those the result here will be slightly optimistic. We checked the engine against textbook results: $1,000 at 5% compounded yearly for 10 years grows to $1,628.89, and $100 a month at 5% compounded monthly for 10 years grows to $15,528.23.

Using the inflation field

A balance that doubles over twenty years hasn't doubled your spending power if prices rose too. Enter an inflation assumption to add a third line to the chart: your balance in today's money. For context on past inflation, the Inflation calculator uses official consumer price index data for each country.

Things this calculator doesn't do

  • It doesn't apply tax. Interest may be taxable unless it's in a tax-advantaged account (such as an ISA in the UK, a TFSA in Canada or certain US retirement accounts).
  • It assumes a constant rate. Variable-rate accounts will drift, and investments in shares or funds go down as well as up.
  • It ignores fees and withdrawals.

Sources

Results are estimates based on the figures you enter and the stated assumptions. They are not financial, tax, legal or engineering advice. Spotted a problem? Tell us.