DAYS360 in Google Sheets: Compare US and European 30-Day Month Rules
Understand Google Sheets DAYS360 methods with explicit month-end controls, compare convention counts with actual dates and preserve uncertain February cases.
Verification status: See the evidence and test scope described in this guide. How formula examples are checked
Quick answer: DAYS360(start_date,end_date,[method]) calculates a day count under a 360-day-year convention. It is not an ordinary elapsed-day calculation. Google documents method 0 or omission for the US rule and other method values for the European rule; examples use explicit 0 and 1.
Availability and version history
- Introduced: first introduction date is not established by the official history reviewed; no desktop release number is inferred.
- Availability: documented in the rolling Google Sheets service; these examples use the web worksheet workflow.
- Checked: October 14, 2026; official DAYS360 reference. Documentation and independent models, with no native Google Sheets execution or wider client certification.
Syntax and purpose
=DAYS360(start_date, end_date, [method])
Supply numeric dates, date-valued cells or DATE expressions. The start date comes first, unlike the end-first argument order of DAYS. The optional method defaults to 0.
Use this function only when the specified calculation actually calls for its day-count convention. A financial contract, accrual policy or another spreadsheet may require a different convention. These examples explain the formula; they do not select terms for a real financial agreement.
The documented adjustments
Google’s US description changes a last-day-of-month start to day 30 and gives a conditional adjustment when the end is day 31. Its European description replaces a day numbered 31 at either endpoint with day 30.
The US paragraph’s final “otherwise” wording is broad enough to be confusing outside the day-31 condition. The controls below use clear ordinary-date and explicit day-31 cases. February and other disputed shorter-month combinations remain unverified rather than being generalized from that prose.
Example 1: an ordinary monthly interval
=DAYS360(DATE(2026,1,15),DATE(2026,2,15),0)
=DAYS360(DATE(2026,1,15),DATE(2026,2,15),1)
Both convention counts are expected to be 30. The actual elapsed calendar interval is 31 days. A 30-day result is therefore intentional under the selected model, not a missing calendar day to add back manually.
From January 15 to March 15, both convention counts are 60, while the actual interval in 2026 is 59 days. The direction of the difference can change with the dates.
Example 2: a day-31 endpoint distinguishes the methods
=DAYS360(DATE(2026,1,29),DATE(2026,1,31),0)
=DAYS360(DATE(2026,1,29),DATE(2026,1,31),1)
Expected outputs are 2 and 1. Under the stated US rule, an end at day 31 with a start before day 30 advances to the first of the next month. Under the European rule, January 31 becomes January 30.
The ordinary calendar interval is two days. That numerical coincidence with the US result does not mean DAYS360 generally reproduces elapsed days.
Advanced example: a one-day calendar interval can have zero convention days
=DAYS360(DATE(2026,1,30),DATE(2026,1,31),0)
=DAYS360(DATE(2026,1,30),DATE(2026,1,31),1)
Expected convention counts are 0 and 0. Both adjusted endpoints are day 30 in these controls, even though the actual dates are one day apart.
If a task counts attendance, reservations or elapsed service days, this is a strong indication that the requested rule is a calendar count rather than this convention. Use the appropriate date-difference or NETWORKDAYS model instead.
Advanced example: inspect a year-end interval
=DAYS360(DATE(2026,1,1),DATE(2026,12,31),0)
=DAYS360(DATE(2026,1,1),DATE(2026,12,31),1)
Expected outputs are 360 and 359. The US day-31 adjustment moves the end to January 1 of the following year, while the European adjustment uses December 30.
If a separate, explicitly selected calculation divides these convention counts by 360, the fractions are 1 and approximately 0.9972222222. That arithmetic does not establish which method a particular agreement requires.
Advanced check: isolate month-end and ordinary reversals
January 31 to March 31, 2026 gives an expected 60 under both methods, compared with 59 actual calendar days. Both adjusted month-end day numbers are 30.
For the ordinary dates February 15 back to January 15, the independently modeled convention difference is -30. This ordinary reversal is not a promise of a universal sign identity across all asymmetric month-end adjustments. Keep native tests for those more complicated reversals separate.
Parsing and unresolved cases
Google warns that slash expressions inside a formula are arithmetic. Its displayed quotients for 10/10/2000 and 10/10/2001 contain decimal-place errors; the actual values are 0.0005 and approximately 0.000499750125. DATE-generated controls avoid that issue.
No complete text, Boolean, fractional-timestamp, historical-date or invalid-method error table is established here. February month-end outputs are deliberately held. Preserve the chosen method in a visible input cell when adapting a workbook, and verify the governing convention before relying on a financial result.
References and verification
Examples use fictional inputs, English function names and comma argument separators. Expected outputs are independently modeled from the cited rules, not native Sheets captures. Check the spreadsheet locale when reproducing punctuation-sensitive formulas.