Date Calculator

An advanced tool for calculating the difference between two dates in days, months, and years. The date calculator allows you to easily determine the duration between past or future dates. Perfect for birthdays, anniversaries, special occasions, project deadlines, and business day calculations.

Start Date

Day

Month

Year

End Date

Day

Month

Year

How to Calculate Dates?

1. Select the start date (day, month, and year)
2. Select the end date
3. Click the "Calculate Dates" button
4. The results will show:
- Total number of days between dates
- Detailed duration in years, months, and days
- Which days of the week the start and end dates fall on

Note: You can calculate the duration between any two dates in the past or future. Dates must be between years 1900 and 2100.

Days Between Two Dates

Use this calculator to find the exact difference between two dates in total days and as years, months, and days.

Total days = end date - start date

Example: March 1, 2026 to March 10, 2026 = 9 days.

Common search phrases:

days between two dates, date difference, how many days between dates, and calculate days from date to date.

Date Calculations

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Counting the days between two dates

The gap between two dates has two defensible answers, and picking the wrong one is the single most common source of disputes over deadlines, invoices, and hotel bills. This page explains inclusive versus exclusive counting, then gives the rules that contracts and courts actually apply.

Formula

exclusive days = end - start | inclusive days = (end - start) + 1

This calculator reports the exclusive count, which is the standard for durations. Add one when you need to count both endpoints as whole days.

Inclusive or exclusive: pick before you count

From 1 March to 5 March is 4 days if you are measuring elapsed time, and 5 days if you are counting how many dates are involved. Neither is wrong; they answer different questions.

The reliable test is to ask what a single day would produce. A hotel stay from Monday to Tuesday is one night, so hotels count exclusively. A conference running Monday to Tuesday is two days, so attendance counts inclusively.

Exclusive (end minus start): interest accrual, hotel nights, project durations, notice periods, age.
Inclusive (add one): event days, leave and holiday entitlement, sentence lengths, shift rosters.
Neither: business-day counts, which drop weekends and holidays before either rule is applied.

How deadlines are actually counted in law

Most legal systems converge on the same three conventions, which is useful because they are rarely stated explicitly in the contract you are reading.

The day the triggering event happens is not counted. A 30-day notice served on 1 April expires at the end of 1 May, not 30 April.
The last day is counted in full, usually to midnight or to the close of business, depending on the instrument.
If the last day falls on a weekend or public holiday, the deadline typically rolls forward to the next working day. It does not roll backward.

Why weeks and months are not interchangeable

A week is always exactly 7 days, so week counts are unambiguous. A month is not: it is 28, 29, 30, or 31 days, which means "3 months" and "90 days" are different periods almost every time.

From 31 January, three months forward is 30 April by the end-of-month convention, which is 89 days. Ninety days forward is 1 May. If a contract says "90 days" and you calculate in months, you will be a day out - and interest, penalties, or limitation periods may hinge on it.

Worked example

An invoice is dated 14 November 2025 with net-45 terms. Counting exclusively from the invoice date, day 45 lands on 29 December 2025.

Cross-check with the calendar: 16 days remain in November, plus 29 days into December, which is 45. Because 29 December 2025 is a Monday and not a public holiday in most jurisdictions, no roll-forward applies. Payment is due that day.

Fixed date intervals worth memorising

Interval	Days	Note
1 week	7	Always exact
1 fortnight	14	Always exact
1 month	28-31	Depends on the month, never fixed
1 quarter	90-92	Q1 is 90 days, or 91 in a leap year
1 common year	365	Any year not divisible by 4
1 leap year	366	Divisible by 4, except centuries not divisible by 400
4 years	1,461	Includes exactly one leap day in almost all cases

1900 was not a leap year and 2100 will not be, because century years must be divisible by 400 to qualify.

Frequently Asked Questions

No, it reports calendar days. Business-day counting requires knowing which holiday calendar applies, and holidays differ by country, region, and sometimes by industry, so a generic answer would be misleading.

Because the gap rarely divides evenly by 7. A 45-day gap is 6 weeks and 3 days, shown as 6.43 weeks. The whole-week figure plus the remainder is usually the more useful reading.

The end-of-month convention applies: 31 January plus one month is 28 or 29 February, not 3 March. This calculator follows that convention, as do most accounting systems and the ISO 8601 duration model.

The arithmetic will run, but the result assumes a proleptic Gregorian calendar. Historical records before Gregorian adoption used the Julian calendar, and adoption dates ranged from 1582 in Catholic Europe to 1752 in Britain and 1923 in Greece. Expect a discrepancy of 10 to 13 days.

Not for a date-to-date count. Daylight saving shifts the length of a specific day by an hour but does not add or remove calendar dates. It only matters when you are measuring a duration in hours, not in days.

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References

Last reviewed: 2026-08-07. This page is informational. For legal, medical, tax, or financial decisions, confirm the result with a qualified professional.