Compound Interest Calculator
This Compound Interest Calculator turns the figures for compound Interest into a result you can review. Try realistic inputs and keep the time period, rate and units consistent.
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Last reviewed January 15, 2026 — see our editorial & accuracy policy.
Method: Future value = P(1 + r/n)^(nt) plus the future value of any regular contributions, compounded at the frequency you select.
How it works
The compound interest formula for a lump sum is:
A = P × (1 + r ÷ n)n × t
where A is the final amount, P is the principal, r is the annual rate, n is the number of compounding periods per year and t is the number of years. When you add regular monthly contributions, each deposit also earns compound interest for the remaining time.
How to use the Compound Interest Calculator
Enter the values requested by the tool and start with one realistic example. Read the result together with its unit or label, then change one input at a time if you want to compare options. Keeping a note of the original figures makes the calculation easier to check later.
Use the result as a planning estimate rather than a quote or guarantee. Rates, fees, tax rules and personal circumstances can change the final figure.