Date Calculator - Add or Subtract Days, Weeks, Months, Years

    Pick a date, add 90 days, get the answer. Works with days, weeks, months, and years - forward or backward. Shows the resulting date, day of the week, and a breakdown of elapsed time.

    Parameters

    Enter data for calculations

    Choose whether to add or subtract time

    Select the starting date from the calendar picker.

    Select a time unit

    Enter a positive number (1-10,000)

    Form progress0 / 4 fields

    💡 Fill in all required fields to unlock the calculate button

    Pick a date. Add time. Get the result.

    Try it now
    Start date: January 15, 2026. Operation: Add. Unit: Months. Amount: 6.
    Result: Wednesday, July 15, 2026
    Breakdown: 181 days / 25 weeks / 5 months

    Select a starting date, choose a time unit (days, weeks, months, or years), enter a number, and the calculator returns the resulting date with the day of the week. It handles month-end edge cases automatically: adding 1 month to January 31 gives February 28 (or 29 in a leap year), not an impossible February 31. The breakdown grid shows the total gap in days, weeks, and approximate months.

    Supported time units

    Unit How it works Edge case handling
    Days Adds exact calendar days Crosses month/year boundaries automatically
    Weeks Adds multiples of 7 days Same day of the week guaranteed
    Months Moves to the same day in a future/past month If the target month is shorter, snaps to last day (Jan 31 + 1 month = Feb 28)
    Years Moves to the same day and month in a future/past year Feb 29 + 1 year = Feb 28 (non-leap year)

    When this calculator comes in handy

    Contract deadlines
    A 90-day notice period starts March 1. When does it end? Add 90 days - result: May 30.
    Warranty expiration
    Bought a laptop on June 10, 2024. Warranty: 2 years. Add 2 years - expires June 10, 2026.
    Pregnancy due date
    Last menstrual period: January 5. Add 280 days (40 weeks) - estimated due date: October 12.
    Passport renewal
    Passport expires in 6 months. Subtract 6 months from the expiry date to find the latest renewal date.

    Worked examples

    Add 30 days
    Start: February 1, 2026. Add 30 days. Result: Tuesday, March 3, 2026. February has 28 days, so 30 days crosses into March.
    Add 1 month to Jan 31
    Start: January 31, 2026. Add 1 month. Result: Saturday, February 28, 2026. The calculator snaps to the last day of February since Feb 31 does not exist.
    Subtract 1 year from a leap day
    Start: February 29, 2024. Subtract 1 year. Result: Tuesday, February 28, 2023. Since 2023 is not a leap year, the result is Feb 28.
    Add 52 weeks
    Start: June 20, 2026 (Saturday). Add 52 weeks. Result: Saturday, June 19, 2027. Same day of the week, 364 days later (not exactly 1 year).
    Subtract 100 days
    Start: June 20, 2026. Subtract 100 days. Result: Wednesday, March 12, 2026. The breakdown shows 100 days / 14 weeks / 3 months.

    FAQ

    What happens when I add 1 month to January 31?
    The calculator moves to February 28 (or 29 in a leap year). Since February has fewer than 31 days, the result snaps to the last valid day of the target month. The same logic applies to adding months to the 30th when the target month has only 28-29 days.
    Is adding 12 months the same as adding 1 year?
    Almost always, yes. Both move the date to the same month and day one year later. The only edge case is leap day: adding 12 months to February 29 gives February 28 of the next year, and adding 1 year does the same. The result is identical.
    Why is 52 weeks not exactly 1 year?
    52 weeks = 364 days, but a regular year has 365 days (366 in a leap year). So adding 52 weeks lands one day short of the same date next year. If you need exactly one year, use the "Years" unit instead of weeks.
    Can I enter more than 10,000 units?
    The calculator accepts values from 1 to 10,000. For most practical purposes this is more than enough - 10,000 days is over 27 years. If you need to go further, use the "Years" unit: 10,000 years will take you well beyond any practical date.
    How is the "months" value in the breakdown calculated?
    The breakdown grid divides the total number of days by 30.44 (the average length of a month in the Gregorian calendar) and rounds down. This gives an approximate month count. For an exact month count, use the Date Difference Calculator which computes calendar months precisely.

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