Formula
Day difference = (end date at UTC midnight − start date at UTC midnight) ÷ 86,400,000 milliseconds.
Time & Date
Date Difference Calculator
Count the calendar days between two dates using year, month and day inputs.
Calculator
Working calculator
Live result30 daysElapsed days, start date counted as day zero
Formula used
Day difference = (end date at UTC midnight − start date at UTC midnight) ÷ 86,400,000 milliseconds.
This is the method behind the answer, so the result can be checked rather than simply trusted.Printable calculation report
Result: 30 days. Assumption: The start date is not counted as a full elapsed day.
- Start year
- 2026
- Start month
- 5
- Start day
- 15
- End year
- 2026
- End month
- 6
- End day
- 14
- Page/date context
- 2026-05-16 UTC page version
- Page URL
- https://calculationtime.com/calculators/date-difference-calculator
Worked example
15 May to 14 June spans 30 elapsed midnights. Counting the start date inclusively would produce 31 calendar dates touched, which is a different question.
Professional note
Contracts, subscriptions, visas and legal deadlines may use inclusive counting or local close-of-business rules. Confirm the rule before relying on a date count for compliance.
Regional and unit assumptions
Inputs use numeric year, month and day fields to avoid ambiguity between DD/MM and MM/DD formats.
Assumptions and limitations
- The start date is not counted as a full elapsed day.
- Dates are evaluated at UTC midnight to avoid daylight-saving hour shifts.
- Invalid calendar dates are normalised by the JavaScript Date model, so check unusual month/day combinations carefully.
Methodology & Accuracy
How this calculator is checked
CalculationTime pages are built around visible arithmetic: the formula, assumptions, worked example and practical limitations are shown so the result can be checked rather than simply trusted.
Formula used
Day difference = (end date at UTC midnight − start date at UTC midnight) ÷ 86,400,000 milliseconds.
Standard or basis
Inputs use numeric year, month and day fields to avoid ambiguity between DD/MM and MM/DD formats.
Where a calculator follows a named legal, trade or industry standard, that standard is cited visibly. Otherwise the page uses transparent general arithmetic and states its limits.Master's Tip
Contracts, subscriptions, visas and legal deadlines may use inclusive counting or local close-of-business rules. Confirm the rule before relying on a date count for compliance.
Related calculators
Questions
Does the calculator include the start date?
No. It measures elapsed days. Inclusive calendar counting is a separate convention.
Why use UTC?
UTC midnight avoids daylight-saving changes adding or removing an hour from a local day calculation.
Can this calculate business days?
Yes. Use the related business days calculator when you need Monday-to-Friday weekday counting instead of elapsed calendar days.