⏱TimeCalcLab

Date Add & Subtract Calculator

Add or subtract days, weeks, months or years from any starting date to find the resulting calendar date. Use any combination of the four duration fields, with true calendar arithmetic that respects real month lengths and leap years. Everything updates instantly and runs in your browser.

Operation

Result date

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Enter a starting date to see the result.

Example: March 15, 2026 + 1 year, 2 months, 10 days = May 25, 2027.

How to Use the Date Add & Subtract Calculator

  1. Choose your starting date.
  2. Choose Add or Subtract.
  3. Enter any combination of years, months, weeks and days (blank means zero).
  4. Read the result date, the day of the week and a summary of what was applied.

How to Add Days to a Date

Set the toggle to Add and put the number of days into the Days field, leaving Years, Months and Weeks blank. The calculator adds calendar days using real month lengths. For example, March 1 plus 30 days is March 31, because March has 31 days. Adding days never uses a fixed 30-day month, so the result is correct across short and long months.

How to Subtract Days From a Date

Switch the toggle to Subtract and put the number of days into the Days field. The calculator counts back that many calendar days, crossing month and year boundaries correctly. For example, March 15 minus 14 days is March 1.

How to Add Weeks to a Date

Put the number of weeks into the Weeks field. One week is exactly 7 calendar days, so adding weeks always lands on the same weekday as the starting date. For example, a Monday plus 2 weeks is the Monday 14 days later.

How to Add Months to a Date

Put the number of months into the Months field. Months vary in length — from 28 to 31 days — so the calculator adds real calendar months rather than a fixed number of days. When the starting day does not exist in the destination month, the result clamps to the last valid day of that month. For example, January 31, 2026 plus 1 month is February 28, 2026, because February 2026 only has 28 days. In a leap year such as 2024, January 31 plus 1 month is February 29.

How Leap Years Affect Date Calculations

A leap year contains an extra day, February 29, so the year has 366 days. This matters when adding years to a date of February 29. For example, February 29, 2024 plus 1 year clamps to February 28, 2025, because 2025 is not a leap year. February 28, 2025 plus 1 year is February 28, 2026. A year is a leap year if it is divisible by 4, except century years which must be divisible by 400.

Date Calculator vs Days Between Dates Calculator

This Date Add & Subtract Calculator starts from one date and moves forward or backward by a duration you specify, to find a future or past date. The Days Between Dates Calculator does the opposite: it measures the gap between two dates you already know. Use this tool when you have a start date and a duration; use Days Between Dates when you have two dates and want the difference.

Date Calculator vs Business Days Calculator

This calculator uses normal calendar dates — every day of the week counts, including weekends. The Business Days Calculator skips weekends and your configured non-working days, so it is the right tool when you need a count or target date expressed in working days rather than calendar days.

Common Date Calculation Mistakes

  • Assuming all months have 30 days. Real months range from 28 to 31 days, so a 30-day approximation drifts over long ranges and across February.
  • Forgetting leap years. February 29, 2024 plus one year is February 28, 2025, not February 29, 2025.
  • Month-end overflow. January 31 plus one month is February 28 (or 29 in a leap year), not March 3 — the day clamps to the last valid day of the destination month.
  • DST and timezone errors. This calculator treats inputs as calendar dates and counts in UTC, so daylight saving never shifts a whole-day result.
  • Mixing business days with calendar days. Adding 30 calendar days is not the same as adding 30 business days; use the Business Days Calculator for working-day counts.
  • Counting the starting date incorrectly. Adding 1 day to December 31, 2026 gives January 1, 2027 — the day after the start, not the start itself.

FAQs

How do I add days to a date?
Enter your starting date, leave the toggle on Add, type the number of days into the Days field and leave Years, Months and Weeks blank. The result date updates instantly. For example, March 1 plus 30 days is March 31.
How do I subtract days from a date?
Enter your starting date, switch the toggle to Subtract, type the number of days into the Days field and leave the other duration fields blank. For example, March 15 minus 14 days is March 1.
What date is 30 days from a given date?
Set the toggle to Add, put 30 in the Days field and leave Years, Months and Weeks empty. The calculator adds 30 calendar days using real month lengths, so the result respects months with 28, 30 or 31 days.
What date was 90 days before a given date?
Set the toggle to Subtract, put 90 in the Days field and leave the other fields blank. The calculator counts back 90 calendar days, crossing month and year boundaries correctly.
How do I add weeks to a date?
Put the number of weeks into the Weeks field. One week is exactly 7 calendar days, so adding 2 weeks moves the date forward 14 days and lands on the same weekday as the starting date.
How do I add months to a date?
Put the number of months into the Months field. Months are added using real calendar months, not a fixed 30-day approximation. If the starting day does not exist in the destination month, the result clamps to the last valid day of that month.
What happens when I add one month to January 31?
January 31 plus one month lands on February 31, which does not exist, so the result clamps to the last valid day of February. In a normal year that is February 28; in a leap year such as 2024 it is February 29.
How are leap years handled?
The calculator uses real calendar dates, so February has 29 days in a leap year and 28 otherwise. February 29, 2024 plus one year clamps to February 28, 2025, because 2025 is not a leap year. A year is a leap year if it is divisible by 4, except century years which must be divisible by 400.
Can I add years, months, weeks and days together?
Yes. Fill in any combination of the four fields. The calculator applies years first, then months (each with month-end clamping), then weeks and days together. For example, March 15, 2026 plus 1 year, 2 months and 10 days is May 25, 2027.
What is the difference between calendar days and business days?
Calendar days count every day of the week including weekends. Business days count only working days, excluding weekends and selected non-working days. This Date Add & Subtract Calculator uses calendar days; use the Business Days Calculator for working-day counts.