How the calculator works

  • Interest dates fall every 12, 6 or 3 months counted from the issue date, with the last payment on the maturity date, together with the face value.
  • Each payment is face value × interest rate ÷ payments a year. Tax is taken from each payment.
  • Accrued interest: buying between interest dates, you pay the seller the interest earned since the last payment (days since it ÷ days in the period × one payment). The next payment gives it back in full.
  • Current yield is a year's interest ÷ the price. Yield to maturity is the yearly rate, compounded at each payment, at which every payment you'll receive is worth exactly what you pay today. It counts the gain or loss at maturity, so it's the figure to compare bonds with.

Buying at a price below 100 adds a gain at maturity; above 100, a loss. Either way the interest payments stay the same.