Compound Interest Calculator

Compound interest means you earn returns on both your original deposit and previously earned interest. Adjust principal, rate, compounding frequency, and optional contributions to project growth over time. Everything runs locally in your browser — your inputs are not uploaded to produce the result.

It is how often interest is added to the balance — monthly, quarterly, or annually. More frequent compounding usually grows the balance slightly faster at the same nominal rate. Add regular contributions to model saving into an account or investment over time.

This is a mathematical projection. Markets and savings rates can change, and past performance is not a guarantee. Tweak the inputs above to compare options, then copy or note the result you need.

The projection assumes you never withdraw and the rate never changes. In cash accounts the rate is set by the bank; in investments the “rate” is an assumed average. Fees, tax, and inflation all reduce what you can spend later — lower the rate if you want a more conservative picture.

Compare two terms or two contribution amounts while holding the rest still. That shows whether time or deposits are doing the work. The Savings Calculator is the same family of maths with a monthly-deposit emphasis; Investment Growth adds an inflation-adjusted view.