Compound Interest Calculator
Project your savings growth from a starting balance, monthly contributions and an interest rate.
Year-by-year growth
| Year | Balance | Total contributed | Total interest |
|---|
How the compound interest calculator works
Enter a starting balance, how much you plan to add each month, your annual interest rate, and the number of years to project. Choose how often interest compounds — daily, monthly, or annually — to see how your balance, total contributions, and total interest earned grow year by year.
More frequent compounding produces a slightly higher return for the same headline rate, because each interest payment starts earning interest of its own sooner.
Frequently asked questions
What is compound interest?
Interest calculated on both your original balance and the interest already earned, so your money grows faster over time than with simple interest.
What's the difference between monthly, daily and annual compounding?
It's how often interest is added to your balance. More frequent compounding produces a slightly higher return for the same headline rate, because interest starts earning its own interest sooner.
Does this calculator account for tax on interest?
No, it shows gross growth before tax. Interest earned outside an ISA may be taxable depending on your Personal Savings Allowance — see our ISA Allowance Tracker for tax-free options.
Is the projected balance guaranteed?
No. It assumes a constant rate and constant contributions, which is a simplification — real rates change. Treat it as an illustration and cross-check against your provider's figures.