Compound Interest Calculator
See how an initial amount grows over time, with interest compounding at any frequency — plus what regular contributions add to the final number.
What is compound interest?
Compound interest is interest calculated on both the money you started with and the interest that money has already earned. Each period, the interest earned gets added to the balance, and the next period's interest is calculated on that larger balance — which is why growth accelerates over time rather than staying flat, the way simple interest would.
The formula this calculator uses
For the lump sum: A = P × (1 + r/n)n×t, where P is your initial amount, r is the annual rate, n is how many times per year it compounds, and t is years. If you add regular contributions, this calculator adds their future value on top, using the standard future-value-of-a-series formula at the same annual rate.
Why regular contributions matter
A lump sum compounds on its own, but most real growth in a savings or investment account comes from adding to it regularly. Even modest monthly contributions can end up contributing more to the final total than the initial amount did, simply because each contribution gets more time left to compound than the ones after it.
Does compounding frequency really matter?
Yes, but less than most people expect. Moving from annual to monthly compounding raises the effective return, but the difference between monthly and daily compounding at typical savings/investment rates is usually small. The interest rate and the time horizon matter far more than the compounding frequency.
How to use this calculator
- Enter your initial amount and the annual interest rate you expect.
- Set the duration and how often it compounds.
- Optionally add a regular contribution to see how much faster it grows.
- Read the future value, total contributed, and interest earned — updated instantly.
Frequently asked questions
No. The SIP Calculator uses the simple monthly rate convention (annual rate ÷ 12) that Indian mutual fund SIPs are quoted with. This calculator uses standard compound interest math, which is the convention used by savings accounts, CDs, and most compound interest calculators outside India.
Match what your actual account or investment uses. Most savings accounts and fixed deposits state their compounding frequency; if you're not sure, monthly is a reasonable general-purpose default and won't be far off from daily compounding at typical rates.
Often, yes — especially over long horizons. Because each contribution starts compounding as soon as it's added, contributions made early in a long time horizon can end up growing nearly as much as the original lump sum did.