Compound Interest Calculator
Free compound interest calculator — project future value from principal, rate, tenure and compounding frequency, with optional monthly contributions. Runs in your browser.
Runs entirely in your browser — nothing you enter is uploaded or stored.
How the projection is calculated
The lump sum grows with the classic formula A = P × (1 + r/n)^(n×t), where P is the principal, r the annual rate as a decimal, n the compounding frequency and t the number of years.
Monthly contributions
Regular deposits are treated as a monthly annuity. We convert your compounding rate into an effective monthly rate — (1 + r/n)^(n/12) − 1 — and compound every contribution to the end date, so a monthly plan is valued consistently whatever frequency you pick.
Frequently asked questions
What is compound interest?
Compound interest is interest earned on both your original principal and on the interest already added. Because each period builds on the last, savings grow faster the longer they compound.
What does compounding frequency change?
It sets how often interest is added back to the balance. More frequent compounding (monthly or daily) earns slightly more than annual compounding at the same nominal rate, because interest starts earning interest sooner.
How are monthly contributions handled?
Each contribution is compounded from the month you add it until the end using an effective monthly rate derived from your chosen frequency. The Total invested card shows your principal plus every contribution.
Is this calculator accurate for planning?
It uses the standard compound interest and annuity formulas and is a good estimate. Real returns vary with rate changes, fees and taxes, so treat the result as a projection.