Days 360 Calculator
Count days between dates on the 30/360 basis.
Results update as you type.
How it works
A days 360 calculator counts the number of days between two dates using the 30/360 convention, a simplified day-count method that treats every month as exactly 30 days and every year as exactly 360 days. It answers questions like "how many 30/360 days are there from the settlement date to the coupon date," which is the basis many bonds, mortgages and accrued-interest calculations are quoted against rather than the true calendar count. The reason this convention exists is convenience and consistency. When interest accrues daily but is quoted on a clean annual basis, pretending each month is 30 days and each year is 360 makes the arithmetic uniform: every full month contributes the same number of days regardless of whether it is a 28, 30 or 31-day month. That uniformity is exactly why treasurers, accountants and fixed-income desks adopted it, even though it does not match the real calendar. The US (NASD) variant used here caps the day-of-month at 30 for both endpoints, so the 31st of a month is treated as the 30th. This calculator applies that rule precisely, computing the year, month and capped-day components separately and summing them. Bond analysts pricing accrued interest, loan officers computing per-diem charges, and anyone reconciling a financial system that reports on a 30/360 basis use it to reproduce the exact figure their contracts and software expect.
days360 = (endY − startY) × 360 + (endM − startM) × 30 + (min(endD,30) − min(startD,30))
The count is assembled from three parts rather than a raw calendar subtraction. The difference in years is multiplied by 360, the difference in months by 30, and the difference in the day-of-month numbers is added directly, with each day-of-month first capped at 30 under the US convention. Capping means the 31st behaves as the 30th, so no month ever contributes more than 30 days. Summing the three components gives a day count where every full month is worth exactly 30 days and every full year exactly 360.
Source:Gregorian calendar / ISO 8601
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Worked example
How to use this calculator
- 1
Enter your values
Enter start date and end date.
- 2
Adjust the options
Fine-tune any options to match your situation.
- 3
Read your result
Days (30/360) updates instantly as you type — no button to press.
Frequently asked questions
What is the 30/360 day-count convention?
It is a method that assumes each month has 30 days and each year has 360 days, used widely in bond markets and lending. Instead of counting actual calendar days, it counts standardised days so that interest accrues uniformly across months of different lengths. This makes coupon and per-diem calculations simpler and consistent, which is why many fixed-income instruments and loan agreements specify a 30/360 basis in their terms.
How does the US 30/360 rule handle the 31st?
Under the US (NASD) convention this calculator uses, any day-of-month of 31 is treated as 30 for both the start and end dates. So a date landing on the 31st contributes the same as the 30th, ensuring no month exceeds 30 days in the count. There are stricter variants that also adjust when the start date is the last day of February, but the basic day-capping rule covers the common case.
Why does 30/360 differ from the actual day count?
Because real months have 28 to 31 days, the 30/360 count deliberately ignores those differences and pretends every month is 30 days. Over a period that includes 31-day months or February, the 30/360 figure will differ from the true calendar days between the dates. That is expected: the convention trades calendar accuracy for arithmetic uniformity so that interest per period is even and easy to compute.
Where is the days 360 method actually used?
It appears in corporate and government bond accrued-interest calculations, many mortgage and commercial-loan interest computations, and financial software and spreadsheets, where a DAYS360 function implements it directly. Accountants use it for consistent monthly interest accrual, and treasurers use it when a contract specifies a 30/360 basis. Whenever a document quotes interest on a 360-day year with 30-day months, this is the count it refers to.
Can the result be negative?
Yes. If the end date is earlier than the start date, the components subtract to a negative total, which correctly represents counting backwards in time. For normal use you would enter the earlier date as the start and the later date as the end to get a positive count. A negative figure simply signals that the dates were entered in reverse order relative to the direction you intended to measure.