Day Count Convention30360 calculator
Calculate day count convention30360calculator easily with our free tool. Get practical results, tips, and comparisons for everyday decisions.
Formula
Days = 360(Y2-Y1) + 30(M2-M1) + (D2-D1); Interest = Principal x Rate x (Days/360)
The 30/360 formula counts the number of days between two dates assuming 30-day months and 360-day years. The adjusted day values (D1, D2) depend on the specific convention variant. Interest is then calculated as principal multiplied by the annual rate multiplied by the year fraction.
Frequently Asked Questions
What is the 30/360 day count convention?
The 30/360 day count convention is a method used in finance to calculate accrued interest on bonds and loans by assuming every month has exactly 30 days and every year has exactly 360 days. This simplification makes interest calculations more predictable and easier to compute than counting actual calendar days. The convention is widely used in US corporate and municipal bond markets, mortgage-backed securities, and many fixed-income instruments. Under this method, a six-month period always equals 180 days regardless of whether months have 28, 29, 30, or 31 actual days. This standardization allows consistent interest accrual across different calendar periods and simplifies settlement calculations between bond traders.
When is the 30/360 convention used versus Actual/365?
The 30/360 convention is standard for US corporate bonds, agency bonds, municipal bonds, and many mortgage products. It is the default for most fixed-rate instruments in the US market. The Actual/365 convention (also called Actual/Fixed) counts the real number of days between dates and divides by 365, making it common for US Treasury bonds, UK government gilts, and many money market instruments. The Actual/360 convention is standard for money markets, LIBOR-based instruments, and commercial paper. Euro-denominated bonds typically use Actual/Actual or 30E/360. The choice of convention is specified in the bond indenture or loan agreement and directly affects the amount of interest accrued and paid.
How does the 30/360 convention affect interest payments?
The 30/360 convention creates predictable interest amounts because each month is treated as exactly one-twelfth of a year. For a bond with a $100,000 face value and 6% annual coupon, the monthly accrual is exactly $500 regardless of the month length. With Actual/365, February accrues only $460.27 while a 31-day month accrues $509.59. Over full coupon periods, the differences tend to be small, but they become significant for odd first or last coupon periods, accrued interest calculations at bond settlement, and partial period interest on loans. When buying a bond between coupon dates, the accrued interest calculation using 30/360 versus actual day count can differ by tens or hundreds of dollars on large positions.
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