Add / Subtract Date Calculator
Add or subtract any number of days, weeks, months, or years from a start date to find the resulting date and day of the week — useful for deadlines, due dates, and planning.
Start Date & Offset
Resulting Date
14 August 2026
Friday
+30 days from 15 July 2026
14 August 2026 · Friday
How It Works
This calculator shifts a start date forward or backward by a chosen amount and unit. Adding or subtracting days and weeks is straightforward day-counting that automatically crosses month and year boundaries correctly, including leap years. Adding or subtracting months and years is slightly different: the calculator moves to the same day-of-month in the target month where possible (e.g., 15 March + 2 months = 15 May). When the target month is shorter (e.g., 31 January + 1 month, but February has only 28 or 29 days), the date automatically rolls over according to standard date-arithmetic rules. The result also shows the day of the week, useful for confirming whether a deadline, anniversary, or due date lands on a weekday or weekend.
Formula
Days/weeks: calendar-accurate day arithmetic. Months/years: calendar-month/year rollover (e.g., 31 Jan + 1 month = 28/29 Feb, following JS Date normalization).
Frequently Asked Questions
How do I find the date 90 days from today?
Set the start date to today, choose "Add", enter 90, and select "Days". The calculator instantly shows the resulting date and its day of the week.
What happens when adding a month to the 31st of a month?
If the target month has fewer days (e.g., adding 1 month to 31 January), the date normalizes to the last valid day of that month or rolls into the next month, following standard calendar-date arithmetic — the same behavior most calendar apps use.
Can I subtract time to find a past date?
Yes — switch to "Subtract" and enter the amount and unit (days, weeks, months, or years) to find a date in the past, e.g., "90 days before 15 March 2026."
Does this account for leap years?
Yes — day and week arithmetic automatically accounts for real calendar lengths, including the extra day in leap years (February 29).
What is this useful for?
Common uses include finding contract/warranty expiry dates, loan or subscription renewal dates, project deadlines a fixed number of days out, and confirming what day of the week a future or past date fell on.