Finance & Tax

Compound interest calculator

Explore how reinvesting interest changes a single initial amount over time. Compare annual, semiannual, quarterly, monthly and daily compounding at the same nominal annual rate. The result separates the initial principal from the modeled interest earned, without assuming future returns are guaranteed.

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Result

A QUICK GUIDE

How to use

Enter a positive principal, a nominal annual rate (%) and a whole number of years, then select how often interest is reinvested.
After calculating, inspect each year’s opening balance, interest earned and closing balance. Use Previous/Next for long terms and download all years as CSV. This is investment growth, not a loan repayment schedule.
The formula is A = P × (1 + i/m)^(m × t), where i is annual rate divided by 100, m is periods per year and t is years. Earned interest is A − P. This follows repeated multiplication of the balance by 1 + i/m.
Available frequencies are 1, 2, 4, 12 and 365 periods per year. Daily means exactly 365 periods every year, including leap years. The nominal rate is fixed and divided equally across periods.
Principal must be positive and at most 1,000,000,000,000,000; rate 0–1,000%; term 1–100 whole years. Displays use two decimal places; interest is not rounded each period. Extremely large results are rejected.
Model reviewed 2026-10-20. Jurisdiction-neutral mathematical illustration; no tax or investment-product rules. Excludes additional deposits, withdrawals, fees, taxes, inflation and variable returns. This is a scenario, not a forecast or a guarantee.

Yearly compound growth

Amounts display two decimals. Calculations use unrounded values, so displayed rows may not add up exactly. Download all rows as CSV.

Opening balance, yearly interest and closing balance
Year	Opening balance	Interest earned	Closing balance

Download full CSV

Worked examples

Principal 1,000; annual rate 10%; 2 years; annually

Final balance 1,210.00; interest 210.00

The first year earns 100; the second earns 110 because the first year’s interest is reinvested.

Principal 1,000; annual rate 0%; 5 years; monthly

Final balance 1,000.00

Changing compounding frequency has no effect at a zero rate.

Questions & answers

What is the difference between nominal and effective annual rates?

The nominal rate is divided by the number of periods. At a positive rate, reinvesting during the year produces an effective annual rate of (1 + i/m)^m − 1, which is higher than i when m is greater than one.

Can I include monthly deposits?

No. This tool models one initial amount only. Regular deposits need a separate cash-flow model with deposit timing assumptions.

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