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Compound Interest Calculator

A free online compound interest calculator that shows how an initial investment grows over time with compound interest and optional regular contributions. Choose annual, semi-annual, quarterly, monthly, daily, or continuous compounding, and see your final balance, total contributions, and total interest earned — visualized on a growth chart showing principal vs. interest over time.

How the Compound Interest Calculator works

Enter an initial investment, an annual interest rate, and a compounding frequency, plus an optional regular contribution and how often it's added. The calculator simulates your balance month by month, applying interest at the equivalent monthly rate for whichever compounding frequency you chose, and adding contributions at the start or end of each period as selected.

Why compounding frequency matters

The same nominal annual rate produces a slightly higher return the more often it compounds — daily compounding earns marginally more than monthly, which earns more than annual, because interest starts earning its own interest sooner. Continuous compounding represents the mathematical limit of compounding infinitely often, using the formula A = Pert.

How contributions are added

Regular contributions can be added monthly or annually, and at the beginning or end of each compounding period. Contributing at the beginning of a period lets that contribution earn interest immediately, producing a slightly larger final balance than contributing at the end of the same period.

Visual growth chart

See your balance grow year by year on an interactive area chart, with total principal (your deposits) and total interest stacked so you can see exactly how much of your final balance came from each.

Common Mistakes to Avoid

Assuming compounding frequency barely matters

Solution:

Over long time horizons or high rates, the difference between annual and daily compounding can add up to a meaningful amount — always check which frequency your actual account uses.

Forgetting to include regular contributions

Solution:

A lump sum alone understates most real investment growth — most savers add money regularly, and even modest monthly contributions can outgrow the initial investment over long periods.

Confusing 'total contributions' with 'total interest earned'

Solution:

Total contributions is money you put in yourself; total interest earned is what compounding actually generated for you — the final balance is the sum of both plus your initial investment.

Entering the rate as a decimal instead of a percentage

Solution:

Enter the rate the way it's usually quoted — e.g. 7 for 7%, not 0.07. The calculator already divides by 100 internally.

Not accounting for contribution timing

Solution:

Contributing at the beginning of each period rather than the end gives that money extra time to earn interest — over many years this small difference compounds into a noticeably larger balance.

Ignoring taxes, fees, and inflation

Solution:

This calculator computes pure compound growth on the numbers you enter — it doesn't account for taxes on investment gains, account fees, or the effect of inflation on purchasing power.

Frequently Asked Questions

Compound interest is interest calculated on both the original principal and all interest earned so far, so the amount grows faster the longer it compounds — unlike simple interest, which is only ever calculated on the original principal.
More frequent compounding (daily vs. monthly vs. annual) earns marginally more for the same nominal rate, because interest starts earning its own interest sooner. Continuous compounding is the mathematical limit of this effect.
Yes — enter a contribution amount, choose monthly or annual frequency, and choose whether it is added at the beginning or end of each period.
Money contributed at the start of a period earns a full period of interest before the next contribution is added, while money contributed at the end earns none that period — over many periods this adds up.
When there are no additional contributions, the calculator shows exactly how much more your final balance is compared to the same principal, rate, and time under simple interest.
No — it calculates pure compound growth on the principal, rate, and contributions you enter. Real accounts may also involve taxes, fees, or inflation that this calculator doesn't include.
No — every calculation runs locally in your browser. Nothing you enter is uploaded, logged, or stored on any server.

Free Online Compound Interest Calculator

See exactly how an investment grows with compound interest. Enter your initial investment, interest rate, compounding frequency, and time period — add optional regular contributions to model real-world saving and investing.

What You Get

  • Final balance, total contributions, and total interest earned
  • Choice of annual, semi-annual, quarterly, monthly, daily, or continuous compounding
  • Optional regular contributions, monthly or annually, added at the start or end of each period
  • A deposits-vs-interest visual breakdown
  • A year-by-year growth table showing contributions, interest, and balance
  • A comparison against simple interest, showing exactly how much more compounding earns you

Who Uses This Calculator

Savers and investors projecting how a lump sum or regular contributions will grow, students learning how compounding works, and anyone comparing compounding frequencies or the impact of contributing early versus late in each period.