The Excel DAYS360 function counts the days between two dates on the 30/360 convention — the accounting fiction that every month has 30 days and every year has 360. Bonds, loan schedules, and lease accruals are often quoted this way because it makes a month’s interest the same regardless of whether it is February or July. For real calendar days, use DAYS; DAYS360 is specifically for when the contract says 30/360.
TRUE as a third argument for the European method: =DAYS360(A2, B2, TRUE).
Syntax
| Argument | Description | |
|---|---|---|
start_date | Required | The beginning of the period. (Start first — unlike DAYS.) |
end_date | Required | The end of the period. If earlier than the start, the result is negative. |
method | Optional | FALSE or omitted = US (NASD) method · TRUE = European method. The two differ only in how they handle dates falling on the 31st (and month-end February dates, in the US method). |
Available in: every version of Excel. The 30/360 day count is also the default basis of YEARFRAC — =YEARFRAC(A2,B2) is essentially =DAYS360(A2,B2)/360.
30/360 counting in action
Three date pairs, counted three ways — notice how the 30-day-month fiction bends the numbers:
| A | B | C | D | E | |
|---|---|---|---|---|---|
| 1 | Start | End | US 30/360 | European | Actual days |
| 2 | 01/15/2026 | 03/31/2026 | 76 | 75 | 75 |
| 3 | 01/31/2026 | 07/31/2026 | 180 | 180 | 181 |
| 4 | 01/01/2026 | 12/31/2026 | 360 | 359 | 364 |
Row 3 is the convention’s whole point: January 31 to July 31 is exactly six 30-day months — 180 days — even though 181 real days passed. A bond paying interest on the 31st earns the same per month as one paying on the 30th.
The classic application — simple interest accrued on a 30/360 loan:
Try it: interactive DAYS360 demo
Pick two dates and compare the US method, the European method, and the actual day count side by side. Dates on the 31st are where the fun is.
US (NASD) vs. European: what actually differs
Both methods turn the calendar into twelve 30-day months; they only disagree about dates that land on the 31st:
- European (
TRUE): simple — any start or end date on the 31st is treated as the 30th. Done. - US / NASD (
FALSEor omitted): a start date on the 31st (or the last day of February) becomes the 30th. An end date on the 31st becomes the 30th only if the start date was on the 30th or 31st; otherwise it rolls forward to the 1st of the next month — which is why US counts sometimes come out one day higher than European ones.
Which one do I use? Whichever the contract or bond prospectus specifies — this is a legal convention, not a math preference. US 30/360 dominates American corporate bonds and agency securities; 30E/360 (the European method) is common in Eurobond markets.
Errors & common pitfalls
Pitfall: using DAYS360 for real-world day counts. It is off by up to a few days from the calendar by design. Ages, deadlines, days-until-launch — anything human-facing — should use DAYS or plain subtraction. DAYS360 belongs in financial documents that name the 30/360 convention.
Pitfall: forgetting which method you are on. The default is the US method, and the silent one-day differences around month-ends are exactly the kind of discrepancy that makes two analysts’ accrual schedules disagree by a few dollars. State the method explicitly — write FALSE or TRUE rather than omitting the argument.
#VALUE! — an argument isn’t a recognizable date. Text masquerading as a date is the usual culprit. Build dates with DATE or verify with ISNUMBER.
Pitfall: February is weird in both methods. February 28 to March 31 spans 31 real days but can count as 33 under 30/360 (Feb 28 + 2 phantom days). The convention smooths months at the cost of odd individual periods — expected behavior, not a bug.
Practice workbook
Frequently asked questions
What is the 30/360 day count convention?
What's the difference between the US and European methods?
When should I use DAYS360 instead of DAYS?
How do I turn a DAYS360 result into a fraction of a year?
=YEARFRAC(start, end, 0), whose default basis 0 is the same US 30/360 count. Basis 4 of YEARFRAC matches the European method.Why does DAYS360 give 360 for a full year instead of 365?
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