Date Reference Calendar

Bond and loan interest

Calculate bond coupon accrual or simple loan interest between two dates. Compare the supported day-count conventions.

Use a decimal point or comma, without thousands separators. Zero principal gives zero interest; negative rates are allowed. Currency sets rounding (KWD: 3 decimals), not the day-count rule.

Bond coupons and day-count conventions

A bond coupon is an interest payment. For a fixed-rate bond using one of the supported conventions, enter the bond’s face value and annual coupon rate. To calculate interest accrued within a coupon period, use that period’s accrual start date and the date you want to calculate up to.

For coupon schedules, ex-coupon terms or Actual/Actual ICMA, switch to Bond accrual at settlement above.

Simple interest = amount × annual rate / 100 × day-count fraction. The start date is included and the end date is excluded. Actual conventions count calendar days; 30/360 conventions use adjusted day numbers.

Example: 100,000 at 5% from 1 January to 1 February 2026, using Actual/365 Fixed: 100,000 × 0.05 × 31 / 365 = 424.66, rounded to two decimal places.

Supported conventions and limitations
Actual/360
Actual elapsed days divided by 360.
Actual/365 Fixed
Actual elapsed days divided by 365, including in leap years.
Actual/Actual ISDA
Each calendar year is counted separately: days in a leap year / 366, other days / 365.
30E/360
Both dates use day 30 instead of day 31. February has no special adjustment.
30/360 Bond Basis (ISDA)
Start day 31 becomes 30. End day 31 becomes 30 only when the original start day is 30 or 31. February has no special adjustment.

30/360 Bond Basis (ISDA) maps to ISDA 2006 section 4.16(f) and Strata THIRTY_360_ISDA. It is not 30U/360 (US/SIA), which has February end-of-month rules. 30E/360 changes day 31 to 30; 30E/360 ISDA also adjusts February month ends, except a maturity date in February. Actual/Actual ICMA and 30E/360 ISDA require schedule or maturity context and are available in bond mode. Actual/365L is not offered.

The amount and annual rate are constant over the period. This is not a compound-interest, statutory late-interest or bond-pricing calculator. Decimal inputs use exact arithmetic; only the final interest amount is rounded, half away from zero, to the currency’s decimal places.

For an overdue invoice, use a calculator that applies the relevant statutory rates over time: late-payment interest calculator.

Rule reference: OpenGamma Strata — Day Counts. Calculation version 1.

Dedicated to Nullkupong-N1k0 ❤️