Compounds interest on a principal sum between two dates. Enter the principal, the start and end dates, the rate — either a fixed rate (expressed per year by default, or per quarter / month / week / day), or a margin above the Bank of England base rate — and how often interest compounds (daily, weekly, monthly, quarterly or annually). For simple (non-compounding) interest, use the Interest Calculator. Day count is actual/actual; a base-plus-margin rate tracks the Bank of England base rate as it changed over the term, capitalising at each rest.