30E/360: Definition & Meaning | Bondfish
30E/360 is a day-count convention that assumes every month has 30 days and every year has 360 days when calculating how much interest a bond has earned between two dates. It is also known as the “Eurobond basis.”
What it means
Bond markets need a rule for counting the days between coupon payments, and 30E/360 is one of the most common. Under this convention, if either the start date or the end date of the period falls on the 31st of a month, it is treated as the 30th. Every month therefore counts as exactly 30 days, and a full year counts as 360.
The “E” stands for European: the convention is standard in the Eurobond market and appears in the 2006 ISDA Definitions. It differs from the U.S. version of 30/360 in one detail — 30E/360 always trims the 31st back to the 30th for the end date, while the U.S. rule only does so if the start date was also adjusted.
Why it matters for bond investors
The day-count convention determines the exact accrued interest you pay or receive when a bond changes hands between coupon dates, and it feeds into yield to maturity calculations. Two bonds with identical coupons can accrue slightly different amounts of interest simply because their documentation uses different conventions, so always check which one applies before comparing quotes.
Example
Days = 360×(Y2−Y1) + 30×(M2−M1) + (D2−D1), with any 31st counted as the 30th.
From 31 January to 31 July: both dates become the 30th → 30×6 + 0 = 180 days → 180/360 = exactly half a year of interest.
Related terms
This definition is for general information only and is not investment advice. Bond investing involves risk, including possible loss of principal.