Date Difference Calculator
Days between two dates — counted both ways, because "Monday to Friday" is four days or five depending on what you are counting.
Runs entirely in your browser. Nothing you enter is uploaded.
Written and maintained by ReadoutKit / Takashi Yamazaki
How this works
The question underneath the question
Counting days between two dates is subtraction. What makes it worth a tool is that the answer people want is not always the subtraction — and the two candidates differ by exactly one, which is small enough to go unnoticed and large enough to matter.
From Monday to Friday, the gap is four days. The number of days involved is five. Neither is a mistake. A hotel bills four nights. A five-day equipment hire covers Monday through Friday inclusive. A notice period of five days starting Monday may end on Friday or the following Monday depending on the rule that defines it.
This calculator prints both numbers, labelled, rather than choosing for you. The choice is a question about your situation, not about arithmetic, and a tool that answers it silently is guessing.
Where the off-by-one actually bites
Inclusive counting is the norm in most legal and contractual settings, where a period of so many days is understood to include the day it begins. Exclusive counting is the norm for durations of occupancy or possession — nights in a hotel, days a vehicle is out. Below, the same five spans run through the same calculation as above, with every answer side by side.
| Span | What it is | Difference | Inclusive | Working days | Broken down |
|---|---|---|---|---|---|
| 2026-03-02 → 2026-03-06 | Monday to Friday | 4 | 5 | 5 | 4 d |
| 2026-04-01 → 2026-04-30 | A 30-day month, end to end | 29 | 30 | 22 | 29 d |
| 2026-01-01 → 2026-12-31 | A full calendar year | 364 | 365 | 261 | 11 m 30 d |
| 2024-02-01 → 2024-03-01 | February in a leap year | 29 | 30 | 22 | 1 m |
| 2026-01-31 → 2026-03-01 | Starting on a month end | 29 | 30 | 20 | 1 m 1 d |
Monday to Friday is 4 or 5 depending on which column you read, and both are correct: 4 is the distance, 5 is the number of days involved. A hotel charges the first, a contract usually means the second. The whole of April is 29 by difference and 30 inclusive, which is why “a 30-day month” and “30 days” are not the same span.
The last two rows are the ones worth staring at. Both are 29 days. One is exactly one month and the other is one month and one day, because the second starts on 31 January and one month from there lands on 28 February. A rule written as “within one month” and a rule written as “within 30 days” do not describe the same deadline, and the gap between them depends on the month you happen to start in.
Interest calculations use their own conventions again, and financial day-count rules (actual/365, 30/360 and their variants) exist precisely because the industry needed to fix an answer to this question rather than argue it per contract. Anywhere money is charged per day, check which end is counted before trusting a figure.
Working days, and the part deliberately left out
The working-day count here removes Saturdays and Sundays across the range, inclusive of both endpoints — the same convention as the NETWORKDAYS function most spreadsheets provide, so the numbers reconcile. A calendar year is 365 days inclusive and 261 working days, so roughly seven-tenths of a year is available before any holiday is subtracted.
Public holidays are not removed, and that is a decision rather than an omission. Holidays vary by country, by region, by year for movable feasts, and by sector for observances that are customary rather than legislated. A built-in list would be correct for one audience, wrong for the rest, and would quietly rot as legislation changed. The universal part — weekends — is handled, and the local part is left visible for you to subtract, along with the weekend count so you can check the arithmetic.
Months are not a fixed number of days
The years-months-days breakdown counts completed monthly anniversaries and then measures what is left in days. It does not divide by 30, or by 30.44, because no actual month is that long and the approximation drifts. The consequence is that a fixed number of days is a different number of months depending on where you start it:
| Start | What it crosses | 90 days later | Broken down |
|---|---|---|---|
| 2026-01-01 | Jan, Feb, Mar — 90 days exactly | 2026-04-01 | 3 m |
| 2026-03-01 | Mar, Apr, May — 92 days | 2026-05-30 | 2 m 29 d |
| 2026-06-01 | Jun, Jul, Aug — 92 days | 2026-08-30 | 2 m 29 d |
| 2026-11-01 | Crossing a year end | 2027-01-30 | 2 m 29 d |
| 2024-01-01 | A leap year | 2024-03-31 | 2 m 30 d |
Ninety days from 1 January is three months to the day. Ninety days from 1 March is two months and 29 days — a day and a half short of three months, because the quarter it crosses is two days longer. If a contract says 90 days and a policy says three months, they agree in exactly one quarter of the year and disagree in the rest.
The other interesting case is month ends. From 31 January to 1 March is one month and one day: one month after 31 January lands on 28 February, since 31 February does not exist, leaving a single day to 1 March. Note what this implies — adding a month and then subtracting one does not return you to where you started. 31 January plus a month is 28 February; minus a month is 28 January. Three days vanish and nothing brings them back.
This is not a flaw in the implementation. It is a property of a calendar with months of unequal length, and it is why well-drafted contracts specify what “one month from” means when the start date is near a month end.
Leap years and time zones
Leap years follow all three rules here: divisible by four, except centuries, except centuries divisible by four hundred. 2000 was a leap year; 1900 was not; 2100 will not be. Any span crossing those boundaries is a place where hand-rolled date arithmetic commonly gains or loses a day.
Time zones are absent by design. A date is not an instant, and attaching a time introduces intervals that change length across daylight-saving transitions — 23 hours in spring, 25 in autumn — which a truncating division turns into an off-by-one. Working on plain calendar dates anchored to UTC removes the possibility. The answer is the same wherever you run it, and nothing about where you are is required to compute it.
Common questions
- Is Monday to Friday four days or five?
- Both, and which one you want depends on what you are counting. The difference between the two dates is 4; the number of days involved is 5. Hotels and vehicle hire charge the first, because you are paying for nights or for possession. Contracts and notice periods usually mean the second, because a period of so many days is normally understood to include the day it starts. This tool shows both rather than picking one, since the same span genuinely has two correct answers.
- Is 90 days the same as three months?
- Only if you start on the right date. Ninety days from 1 January 2026 is exactly three months, but from 1 March it is two months and 29 days, and from 1 June the same. The quarters of a year are 90, 92, 92 and 92 days long, so a deadline written in days and one written in months line up in one quarter and drift apart in the others. If both appear in the same agreement, they are two different deadlines.
- Is Monday to Friday four days or five?
- Both, and the difference is not a rounding question. Four is the gap — subtract one date from the other. Five is the count of days involved, including the start and the end. Hotels charge by the gap, because you occupy four nights. Rental and hire agreements often charge the inclusive count. Notice periods, court deadlines and permit validity all specify one or the other in their own rules. This calculator shows both figures side by side so you pick deliberately rather than by accident.
- Why are public holidays not deducted from working days?
- Because guessing would be worse than not trying. Holidays differ by country, by region within a country, by year for the movable ones, and by industry for the ones that are customary rather than statutory. A built-in list would be wrong for most visitors and would silently go stale. Weekends are the part that is universal, so that is what is removed; subtract your own holidays from the figure shown.
- Does the calculation handle leap years?
- Yes, including the century rule. Years divisible by four are leap years, except centuries, except centuries divisible by four hundred — so 2000 had a 29 February and 1900 did not. This matters for any span crossing 1900 or 2100, and it is a common source of off-by-one errors in hand-written date code.
- Will I get a different answer in a different time zone?
- No. Everything here works on calendar dates with no time attached, anchored to UTC internally. Subtracting two local timestamps across a daylight-saving boundary yields intervals of 23 or 25 hours, and dividing by 24 then truncating loses a day. Treating dates as dates avoids the class of bug entirely, and means nothing about your location is needed to produce the answer.
- What does the years-months-days breakdown mean exactly?
- It counts complete monthly anniversaries from the start date and then measures the remainder in days. From 31 January to 1 March is one month and one day, because one month after 31 January lands on 28 February and there is one day left. This is not the same as dividing the total days by an average month length, and the two will disagree. The breakdown answers "how many whole months have passed", which is what contracts and tenancies usually mean.
Sources
The formulas and rates used by this tool come from the documents below. Rules change; when a figure here disagrees with the source, the source is right.
Figures checked against the sources below on September 1, 2026.
- ISO 8601 — Date and time formatInternational Organization for Standardization
- RFC 3339: Date and Time on the Internet — TimestampsIETF