A date offset calculator answers a narrow question: given one calendar date, what date is a whole number of days or weeks away? You type the start date as YYYY-MM-DD, an integer amount, and a unit of days or weeks. The page returns the result date, the signed day count that was applied, and the English weekday of that result. An amount of zero returns the start date. A negative amount walks backward.
The Date Difference Calculator is the neighboring tool and the opposite job. It takes two dates and returns a day count. This page takes a date and a count and returns a date. Age Calculator is a specialized span from a birth date. Time Duration Calculator measures two clock times on a 24-hour clock. None of those pages moves a date by a typed number of days.
The calendar is the proleptic Gregorian calendar. Dates are civil dates with no time of day. The arithmetic uses UTC so the day cannot slide because of the computer’s zone. A week is exactly seven days. There is no month step, no year step, no business-day mode, and no holiday list. Adding one month is ambiguous on the 31st, so that operation is not offered.
The start field is text so year 0001 and year 9999 can be typed. An impossible date such as 2026-02-29 stops the calculation. The page does not silently roll that date into March.
The start string is read as year, month, and day. It is accepted only when those three numbers are a real civil date in the supported year range. February 29 is accepted in a leap year and rejected otherwise. A year is a leap year when it is divisible by 4, except century years, which are leap years only when divisible by 400.
Weeks are converted before the date moves: days applied = amount × 7. Days stay as the amount itself. The result is that many civil days after the start, or before it when the count is negative. The weekday is the weekday of the result, not of the start, except when the count is zero and the two dates are the same.
If the result would fall before year 0001 or after year 9999, the calculation stops and no date is shown. The amount limits are checked before that. 365001 is rejected as an amount even when a smaller count would have landed inside the year range. 365000 is allowed, and it can still be rejected afterward if that particular start date would leave the year range.
2026-01-01 plus 1 day is 2026-01-02, a Friday, with 1 day applied. The same start minus 1 day is 2025-12-31, a Wednesday, with -1 day applied. The same start plus 2 weeks is 2026-01-15, a Thursday, with 14 days applied. An amount of 0 leaves 2026-01-01, a Thursday, with 0 days applied.
2026-01-31 plus 1 day is 2026-02-01. 2024-02-29 plus 1 day is 2024-03-01. 2024-02-28 plus 1 day is 2024-02-29. 2026-02-29 is rejected because 2026 is not a leap year. 0001-01-01 minus 1 day is rejected. 9999-12-31 plus 1 day is rejected. 2026-01-15 minus 2 weeks returns 2026-01-01.
2026-01-01 + 1 day = 2026-01-02
2026-01-01 - 1 day = 2025-12-31
2026-01-01 + 2 weeks = 2026-01-15This is not a scheduling tool and not a project plan. It will not skip Saturdays, and it will not know that a particular Monday is a public holiday. If you need the number of days between two dates you already have, use the date difference page instead of inventing an offset and checking it.
The arithmetic runs in the browser. The date and the amount are not uploaded, stored, or sent to an API. Clearing the form removes them from the fields. Do not type a case number, a medical date, or any other sensitive identifier into the fields if you would not want it left on the screen.
Proleptic Gregorian dates only, from year 0001 through 9999. A week is exactly seven days. There is no time of day, no time zone, and no month or year step.
Yes. Weeks are converted with a factor of exactly seven before the date moves. There is no separate week-of-year calendar.
2026 is not a Gregorian leap year, so 29 February is not a real date. 2024-02-29 is accepted, and the next day is 2024-03-01.
No. The page rejects that result. It also rejects an amount outside -365000 to 365000 before it moves the date.
Date difference starts from two dates and returns a count. This page starts from one date and a count and returns a date.