Interest Calculator

Work out how a principal grows over time under either simple or compound interest. Enter the starting amount, the annual rate and the term in years — totals and a year-by-year breakdown update as you type.

• Simple or compound — toggle between I = P · r · t and A = P (1 + r/n)^n·t with one click.
• Compounding frequency— annually, semi-annually, quarterly, monthly or daily; pick whatever matches the product you’re modelling.
• Year-by-year breakdown— expand the panel to see the running balance and accumulated interest at the end of each whole year (plus the final partial year if your term isn’t a round number).
• Currency formatted — totals render as GBP with proper thousands separators, so the figures stay readable at every scale.
• Fractional terms — half-year terms like 2.5 work; the breakdown adds a final row at that exact point.