Compound Interest Calculator

How to use the Compound Interest Calculator

Enter your starting principal amount, the annual interest rate, how many years you plan to save or invest for, and how often interest compounds (monthly, quarterly, etc). Click "Calculate" to see your final balance and total interest earned.

What is compound interest?

Compound interest is interest calculated on both the original principal and the accumulated interest from previous periods. Unlike simple interest, which only grows based on the original amount, compound interest grows faster over time because each period's interest is added to the balance before the next period's interest is calculated — often described as "interest on interest."

How compounding frequency affects returns

The more frequently interest compounds, the faster your balance grows, even at the same annual rate. Monthly compounding will produce a slightly higher return than annual compounding over the same period, because interest is calculated and added to the balance more often.

Frequently asked questions

What's the formula used?
This calculator uses the standard compound interest formula: A = P(1 + r/n)^(nt), where A is the final amount, P is the principal, r is the annual interest rate (as a decimal), n is the number of times interest compounds per year, and t is the time in years.

Can I use this for loan interest instead of savings?
This calculator shows growth on a principal amount, useful for savings and investments. For loan repayments with monthly installments, try the Loan / EMI Calculator instead.

Does this account for regular monthly contributions?
Not currently — this calculator shows growth from a single lump-sum principal. Adding recurring contributions may be added as a future feature.

Is my data stored anywhere?
No. This tool is part of the Toolyard collection of free, browser-based utilities. All calculations run locally in your browser — nothing you enter is uploaded to a server or stored anywhere.