How to use the Date Calculator
- 1
Pick a tab: "Days between dates" to measure a gap, or "Add or subtract" to find a future or past date.
- 2
Enter your dates. Both tabs start with today's date, which you can change.
- 3
For a gap, tick "Include the end date" if both the first and last day should count, and list any public holidays to skip.
- 4
For add or subtract, choose the amount, the unit and the direction, then read the result and its weekday.
Inclusive or exclusive: the one-day difference that causes most mistakes
By default the calculator counts the way most software and most legal deadlines do: from the start date up to the end date, without counting the start day twice. From Monday 2 March to Friday 6 March is 4 days. That answers the question "how many nights" or "how many days later".
Ticking "Include the end date" adds one day so that both the first and the last day are counted. The same Monday to Friday becomes 5 days. Use this when every calendar day is a day of something: a hotel package that runs 1 to 7 July, a five-day training course, a period of annual leave, or a sick note that covers both dates written on it.
If you are unsure, read the rule you are working with. Phrases such as "within 30 days of" or "no later than 14 days after" usually exclude the starting day. Phrases such as "from and including" or "for the period 1 to 31 January" include both ends.
How business days and holidays are counted
Business days are Monday to Friday. Saturdays and Sundays are skipped, and so is any date you type into the holiday box, as long as it falls on a weekday. A holiday on a Saturday is not subtracted twice. Paste one date per line in YYYY-MM-DD format, for example 2026-12-25 and 2027-01-01.
Holidays differ by country and often by region, so the calculator does not guess them. Germany's public holidays vary between states, the United States has federal holidays that private employers may or may not observe, and India's list depends on the state and the employer. Copy the official list for the place that matters to your deadline.
Not every country works Monday to Friday. In Saudi Arabia, Qatar, Kuwait and Oman the weekend is Friday and Saturday, and in some other countries Friday is the main day off. If that applies to you, add the extra days to the holiday list or treat the result as a guide.
When you add business days, the start date itself is not counted. Adding 1 business day to a Friday gives the following Monday, and adding 5 business days to a Wednesday gives the next Wednesday.
Month-end dates and leap years
Adding months is trickier than adding days because months have different lengths. The calculator follows the rule used by most banks, payroll systems and programming languages: keep the same day of the month, and if that day does not exist, use the last day of the month instead.
| Start date | Operation | Result | Why |
|---|---|---|---|
| 31 January 2026 | + 1 month | 28 February 2026 | February 2026 has 28 days |
| 31 January 2028 | + 1 month | 29 February 2028 | 2028 is a leap year |
| 29 February 2024 | + 1 year | 28 February 2025 | 2025 has no 29 February |
| 31 March 2026 | − 1 month | 28 February 2026 | Clamped to the month end |
| 31 May 2026 | + 1 month | 30 June 2026 | June has 30 days |
This means adding one month twice is not always the same as adding two months at once. 31 January plus one month is 28 February, and 28 February plus one month is 28 March. 31 January plus two months is 31 March. When the result is moved to a month end, the calculator says so.
Leap years follow the Gregorian rule: years divisible by 4 are leap years, except century years, which must also be divisible by 400. So 2000 was a leap year, 2100 will not be, and 2024 and 2028 are. Day counts across February are always exact.
Common uses, and what this tool should not be used for
Typical situations and the setting that usually fits:
| Situation | Mode | Tip |
|---|---|---|
| Notice period at work (for example 30 or 90 days) | Add days | Check whether your contract counts calendar or working days |
| Schengen 90/180-day visa stays | Days between, include end date | Entry and exit days both count as days in the area |
| Invoice due in 30 days (net 30) | Add days | Some firms treat a weekend due date as the next business day |
| Project or delivery lead time | Add business days | Add the local public holidays for an accurate date |
| Days until an exam, wedding or trip | Days between | Leave the end date unticked for "days to go" |
| How long you have lived somewhere | Days between | Read the years, months and days line |
This is a calendar tool, not a medical or legal one. A pregnancy due date is usually calculated by an obstetrician or midwife as 280 days from the first day of the last period and then adjusted by ultrasound, so please do not rely on a general date calculator for that. Visa rules, tax residency tests and court deadlines also have specific counting rules, so confirm with the official source before relying on a date.
Why time zones and daylight saving don't affect the count
A date calculator that quietly uses clock times can give answers that are an hour short, which then round down to a day short, when a date range crosses a daylight saving change. This one works purely with calendar dates in UTC, so every day is exactly one day long. Today's date comes from your device, so visitors in Auckland and Los Angeles each see their own local date.
Frequently asked questions
How many days are there between two dates?
Enter both dates in the "Days between dates" tab and the total appears instantly. By default the start date is counted and the end date is not, which matches "how many days later". Tick "Include the end date" to count both.
How do I calculate business days between two dates?
The business days figure counts Monday to Friday in your range. To remove public holidays, type them into the holiday box, one per line as YYYY-MM-DD. Holidays that fall on weekends are ignored, so nothing is subtracted twice.
What is 31 January plus one month?
It is 28 February, or 29 February in a leap year. Because February has no 31st, the date is moved back to the last day of the month. This is the same convention used by most banking and spreadsheet software.
Does the calculator include the start date?
It counts from the start date to the end date, so a range from 1 to 2 March is one day. If you need both the first and last day counted, as with a leave period or a hotel booking, tick "Include the end date".
How many weeks are between two dates?
The weeks and days box divides the total number of days by seven and shows the remainder. For example, 100 days is 14 weeks and 2 days.
Can I count backwards from a date?
Yes. In the "Add or subtract" tab, press Subtract and enter the amount. This is handy for working out when to post documents, when a 60-day return window started, or which date was 90 working days ago.
Last updated on November 9, 2026