Compound Interest Calculator
See how much your money grows when interest compounds over time.
How to use the Compound Interest Calculator
- Enter your starting principal.
- Enter the annual interest rate.
- Choose how often the interest compounds.
- Enter the number of years and read off the future value.
A = P × (1 + r/n)^(n×t)
About the Compound Interest Calculator
Compound interest pays interest on interest. This calculator applies A = P × (1 + r/n)^(n×t), where P is your starting principal, r the annual rate as a decimal, n the number of compounding periods per year, and t the number of years. It reports the future value and splits out how much of that total is interest rather than the money you started with.
Compounding frequency is the part most people misjudge. Moving from yearly to monthly compounding at the same nominal rate adds a little; going from monthly to daily adds very little more. The rate and the number of years do almost all the work, which is why the gap between starting early and starting late dwarfs the gap between a good account and a slightly better one.
What it does not account for: it assumes one constant rate for the entire period. Real investment returns move year to year, so treat this as a smooth illustration rather than a forecast. It also assumes you never add to or withdraw from the balance — there is no contribution field, so for regular deposits use the savings goal calculator. And the result is a gross figure: before tax, before platform or fund fees, and before inflation reduces what that sum will buy.
Frequently asked questions
Does more frequent compounding earn more?
Yes, but with sharply diminishing returns. Monthly compounding beats yearly by a noticeable margin; daily beats monthly by a very small one. The rate and the number of years matter far more than the frequency.
Can I add monthly contributions?
Not here — this calculator grows a single lump sum. To work out a regular monthly deposit, use the savings goal calculator, which solves for the payment needed to reach a target.
Is the result before or after tax and inflation?
Before both. It is a gross nominal figure with no tax, fees or inflation applied. Depending on where you live and what wrapper the money sits in, tax may reduce it, and inflation will reduce what it buys regardless.
Can I use it for debt as well as savings?
Yes, if the debt compounds and you are making no repayments — it shows what the balance grows to. For a debt repaid in fixed monthly instalments, the loan calculator is the correct tool.
What is the rule of 72?
A mental shortcut: divide 72 by the annual rate to approximate the years needed to double your money. At 8%, roughly nine years. It is an approximation that works best for mid-range rates — this calculator gives the exact figure.
Guides & articles about this tool
Simple Interest Formula Explained with Examples
The simple interest formula is I = P x r x t, where t is in years. Here’s how it works, what it’s for, and where people usually go wrong.
The Power of Compound Interest, Explained Simply
Compound interest is simple: your money grows faster because you earn interest on interest. The longer it’s left, the bigger the snowball. This explains h…