Date Calculator
Add or subtract days from a start date to find the date before or after it, with weekday, include/exclude start date rules, ISO date, and weekday/weekend counts.
Date Calculator
Add or subtract a number of days from a start date to calculate the date before or after it. See the weekday, ISO date, counting rule, and weekday/weekend breakdown in one place.
Inputs
Updates as you typeUse “exclude start date” for ordinary “days from now” schedules. Use “include start date” when you need the Nth day of a period.
Calculation notes
- The calculator uses calendar dates only; time of day and time-zone conversion are not included.
- Leap years, month ends, and year ends are handled automatically. For example, Feb 28 + 1 day may become Feb 29 or Mar 1 depending on the year.
- If you need the difference between two fixed dates, use the Date Difference Calculator as well.
Enter a start date and day count to see the resulting date here.
Enter a start date and day count to see the resulting date here.
Calculation flow
Range summary
What is the Date Calculator?
The Date Calculator helps you find a date a set number of days before or after a starting date. It is useful for deadlines, delivery estimates, contract periods, anniversaries, and any schedule that starts from a known date.
You can choose whether to include or exclude the start date, which removes a common source of date-counting confusion. Along with the result date, the tool shows the weekday, ISO date, and weekday/weekend split so you can check the result before adding it to a calendar.
Use it for
- Work deadlines – Check the actual date and weekday 7, 14, or 30 days from a start date.
- Contracts and warranty periods – Compare end dates when the start date is included versus excluded.
- Delivery and booking estimates – Calculate how many days after an order or booking a date will fall.
- Anniversaries and challenges – Find the 100th day including today or the date 365 days from a start date.
- Backward planning – Work back 45 or 90 days from a target date to find a preparation start date.
- Weekday checks – See whether the calculated date falls on a weekday or weekend before you finalize a schedule.
Key features
- Add or subtract days – Switch between dates after and before the start date in the same compact screen.
- Include/exclude start date – Separate “today + 1 day = tomorrow” from “count today as day 1” so the result matches your real-world rule.
- Weekday and ISO date – Show a readable date and ISO format side by side for notes, documents, and calendar entries.
- Weekday/weekend breakdown – Estimate how many weekdays and weekend days are inside the counted range.
- Quick examples and copy – Load common examples such as 7 days, 30 days, and 100th day, then copy the result text.
How to use
- Enter the start date – Choose the date you want to calculate from.
- Enter the day count – Type a whole number of days to add or subtract.
- Choose the direction – Select whether you need the date after or before the start date.
- Confirm the counting rule – Choose whether the start date is excluded or counted as day 1.
- Use the result – Review the date, weekday, weekday/weekend count, and copy the result if needed.
Calculation rules
When the start date is excluded, the next calendar day is treated as 1 day after the start. For example, 1 day after April 26, 2026 is April 27, 2026, and 0 days after is the same date.
When the start date is included, the start date itself is day 1. That means the 100th day including today is 99 calendar days away. This is useful for contracts, events, learning plans, and challenges where the first day counts.
This calculator works in date units only and does not include time of day. It moves through calendar dates, so schedules that depend on time zones or daylight saving time should be checked with a time-zone tool as well.
Frequently asked questions
Does “N days after” include the start date?
In everyday usage, “N days after” usually excludes the start date and starts counting from the next day. Some contracts or rules count the start date as day 1, so this calculator lets you choose either method.
Can I calculate 0 days after or before?
Yes. If you enter 0 days, the result stays on the same date regardless of direction. This is also useful for checking the weekday of the start date.
Are leap years and month ends handled automatically?
Yes. End-of-month, end-of-year, and leap-year transitions are handled by the browser’s date engine, so the result moves naturally into the next month or year.
Do weekday counts include public holidays?
No. Weekdays are counted as Monday through Friday only. Public holidays, substitute holidays, and company days off are not included.
Can it calculate the exact difference between two dates?
This page is focused on finding a result date from a start date and day count. If both dates are already known, the Date Difference Calculator is the better tool.
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