When a bond trades between coupon dates, the buyer owes the seller the interest that has accrued since the last payment.
How it works
Face value times the annual coupon rate, times the days since the last coupon divided by 360, gives accrued interest — using the standard 30/360 day-count convention most corporate bonds use.
What this does not include
Some bonds (notably U.S. Treasuries) use an actual/actual day-count convention instead of 30/360 — this calculator uses the more common corporate-bond convention, which can produce a slightly different figure for government securities.
How to use this calculator
- Enter face value, annual coupon rate, and days since the last coupon payment.
Frequently asked questions
Why does the buyer pay the seller accrued interest?
Because the buyer will receive the full next coupon payment covering the entire period, including the days before they owned the bond — accrued interest reimburses the seller for their share of that period.
What’s the difference between “clean” and “dirty” bond price?
The clean price excludes accrued interest; the dirty (or “full”) price includes it — the dirty price is what the buyer actually pays at settlement.
Why 30/360 instead of actual calendar days?
It’s a simplifying market convention that treats every month as having 30 days and every year as 360 days, making calculations consistent regardless of the specific calendar dates involved.
