Date Calculator
Result
Total days
- Years
- 1
- Months
- 0
- Days
- 0
- Total weeks
- 52.1 weeks
A date difference is easy to add up and easy to get wrong. From 31 January to 1 March is 29 days, and most people would call that one month and one day — but adding one month to 31 January gives 28 February, so a naive subtraction that borrows from the month count reports either one month and minus one day, or zero months. This calculator reports the span four ways: total days, total weeks, and the years-months-days breakdown that clamps the way a calendar does.
How long is a day, a week, a month, a quarter and a year
| Span | Days |
|---|---|
| Day | 1 |
| Week | 7 |
| Month | 28 – 31 |
| Quarter | 90 – 92 |
| Year | 365 or 366 |
Only the first two rows are constants. A month is 28 to 31 days and a quarter is 90 to 92, so a span of 90 days is exactly one quarter only when it happens to start in the right month. This is why the breakdown above is computed on the calendar instead of by dividing.
Formula
totalDays = whole days from the start date to the end date; the breakdown takes the largest number of whole months that does not overshoot
- totalDays
- Whole days between the two dates; the start day itself is not counted, the end day is
- totalWeeks
- totalDays divided by 7, kept to one decimal rather than rounded to whole weeks
- months
- Whole months that fit, measured on the calendar rather than as 30-day blocks
- days
- What is left after those whole months — always shorter than the month that follows
Use the calculator to count the days until a deadline, to work out how long a project ran, or to check a figure someone else quoted. The days-only answer is the one to trust; the years-months-days breakdown describes the same span in calendar units, so 365 days reads as one year while 364 days reads as eleven months and thirty days — two numbers that look inconsistent and both describe the truth. What it cannot do is count only working days, or treat a date before 1582 as anything but proleptic Gregorian.
Worked examples
1 January 2026 to 1 January 2027
- Whole days: 2026 is a common year, so 1 January 2026 to 1 January 2027 is 365 days — the start day is not counted and the end day is
- The months walk: one whole year fits and lands exactly on the end date, so years is 1 and both months and days are 0
- Total weeks: 365 ÷ 7 = 52.14, reported to one decimal as 52.1 rather than rounded to 52
- totalDays is the anchor: it is computed first and never derived from the breakdown
The clean case, where the two readings agree exactly. The next example is the one where they do not.
31 January 2026 to 1 March 2026
- Whole days: 28 days of February plus 1 day of March is 29
- One month from 31 January clamps to 28 February, which is still before the end date, so months reaches 1
- Two months from 31 January would be 31 March, past 1 March, so months stops at 1
- The remainder from 28 February to 1 March is 1 day, and the breakdown reads one month and one day
This is the case a borrow-from-the-month subtraction gets wrong: it compares the day numbers 31 and 1, borrows, and reports either one month and minus thirty days or zero months and twenty-nine days. Neither adds back to the end date.
29 February 2024 to 28 February 2025
- 2024 is a leap year and 2025 is not, so the two endpoints are 365 days apart even though the day number drops from 29 to 28
- One year from 29 February 2024 is 28 February 2025 — a year is not a fixed number of days on the calendar
- The walk lands exactly on the end date, so months and days are both 0
- totalDays reads 365, the same as the first example, while every date in the span is one day earlier
A span of exactly 365 days can be one year or not, depending on where it starts. That is why the tool reports both readings rather than choosing one.
Limitations
The breakdown is a description, not a unit conversion. A month is 28 to 31 days, so 30 days can read as one month in one pairing and zero months in another, and the rule here is to add whole calendar months back until the next one would overshoot. Other tools use a different rule and will disagree by a day or two on the same pair. Total days has no such freedom. Nothing here counts working days or skips public holidays.
Frequently asked questions
- How many days are between two dates?
- Count the whole days from the start date to the end date, with the start day not counted and the end day counted. 1 January 2026 to 1 January 2027 is 365 days, because 2026 is a common year. That convention is what makes a same-day span read zero rather than one, and it is the one the other date tools on this site use.
- How many months and days is 31 January to 1 March?
- One month and one day. Adding one month to 31 January clamps to 28 February, which is still short of 1 March, and adding two months gives 31 March, which overshoots. The remainder from 28 February to 1 March is one day. A subtraction that borrows from the month count reports minus thirty days instead.
- Does the count include the start date?
- No, the start date is the day before the count begins and the end date is included. Same-day therefore reads zero, and 1 January to 2 January reads one day. It is the same convention the business days and add-days tools here use, so the numbers on those pages line up with the numbers on this one.
- Why is a year sometimes 365 days and sometimes 366?
- Because the length of a year is not fixed on the calendar, and neither is the length of a month. 29 February 2024 to 28 February 2025 is 365 days and the breakdown calls it one year, because adding one year to the start lands on the end. A span containing a leap day is 366 days and also reads as one year.
- Can I put the later date first?
- Yes, the two endpoints are swapped when the end date is earlier, so the answer is identical either way. A signed difference would be a different tool; this one reports the size of the span, which is what a deadline or a project length needs.
References
- relativedelta — the dateutil module — dateutil project documentation
- ECMAScript Language Specification: Numbers and Dates — Ecma International