Date Calculator
Add or subtract days, weeks, or months from any date. Find the difference between two dates.
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What Is a Date Calculator?
A date calculator adds or subtracts days, weeks, and months from any starting date. It also finds the exact gap between two dates in multiple units. Enter your values and get an instant answer.
Counting days by hand is error-prone around month boundaries and leap years. This tool applies calendar rules automatically so the result is always correct. It shows the answer in days, weeks, and months simultaneously.
Use it to find deadlines, plan events, or convert between date units. The calculator works for dates in the past and future.
How Do You Use This Date Calculator?
Choose a mode: add/subtract time from a date, or find the difference between two dates. Enter your dates and values, then click Calculate.
- Select the mode: add/subtract time or find the difference between two dates.
- Enter the start date using the date picker.
- Type the number of days, weeks, or months to add or subtract (or enter a second date).
- Press Calculate to see the result.
- Read the output date or the difference in days, weeks, and months.
- Adjust any input to recalculate instantly.
How Does the Date Calculator Formula Work?
The formula used: Result Date = Start Date ± (Days + Weeks × 7 + Months)
When adding days the calculator advances the calendar date by exactly that number of days. Adding months moves the month counter forward and clamps the day if the target month is shorter (e.g., 31 January + 1 month = 28 February).
Weeks convert to days via total days = weeks × 7 + days. The difference mode counts every calendar day between the two dates inclusively or exclusively depending on convention.
Leap years and varying month lengths are factored in for every calculation.
What Are Some Example Calculations?
Start date 1 January 2026 + 90 days = 1 April 2026. Difference between 1 January 2026 and 25 December 2026 = 358 days (51 weeks, 1 day).
Project deadline: 60 working-calendar days from 10 March 2026
10 March + 60 days = count through March (21 days left), April (30), May (9 remaining).
9 May 2026.
Difference between 14 February 2026 and 25 December 2026
Feb remaining = 14 days, Mar-Nov = 275 days, Dec 1-25 = 25 days. Total = 314 days.
314 days (44 weeks and 6 days).
Subtract 6 months from 31 August 2026
August minus 6 months = February. Feb has 28 days in 2026 so day clamps to 28.
28 February 2026.
When Should You Use a Date Calculator?
Use this calculator to find delivery dates, contract end dates, or notice-period deadlines. Enter a start date and add the required number of days or months to get the target date.
It is also useful for travel planning and event countdowns. Find exactly how many days remain until a holiday, exam, or anniversary by entering both dates in difference mode.
What Do These Terms Mean?
What Are the Best Tips to Know?
- Add 7 days instead of 1 week to keep inputs in a single unit for clarity.
- Use the difference mode to count remaining days until a deadline or event.
- Remember that adding 1 month to 31 January gives 28 (or 29) February, not 3 March.
- Combine weeks and days for rental or lease calculations (e.g., 52 weeks + 1 day = 1 year).
- Cross-check results against a physical calendar for dates within the current month.
What Mistakes Should You Avoid?
- Confusing calendar days with working days. This calculator counts all calendar days.
- Assuming every month has 30 days when estimating manually.
- Forgetting that subtracting months can clamp the day (e.g., 30 April - 1 month = 30 March, not 31 March).
- Entering dates in the wrong format and misreading the result by a month.
Frequently Asked Questions
How many days are between two dates?
Enter both dates in the calculator and it will count the exact number of days between them, accounting for varying month lengths and leap years.
Does this include weekends and bank holidays?
This calculator counts all calendar days by default. It does not distinguish between working days and weekends.
How do I find a date 30 days from now?
Enter today's date as the start date, set days to 30, and click Calculate. The result shows the exact date 30 days in the future.
What happens when I add 1 month to a date at the end of a long month?
The calculator clamps the day to the last day of the target month. Adding 1 month to 31 January gives 28 February (or 29 in a leap year).
Can I subtract dates to find a negative difference?
The calculator always returns a positive gap. Swap the start and end dates if you want to see the duration in the other direction.
How do I count only working days between two dates?
This calculator counts calendar days. To estimate working days, multiply the number of full weeks by 5 and add any remaining weekdays manually.
Is the calculator accurate across time-zone changes?
The calculator works with dates only, not times. Time-zone differences and daylight saving shifts do not affect the day count.
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