Calendar Calculator

Add or subtract days, weeks, months, or years from a date to find the resulting date and its weekday. Enter the date and the change.

Resulting Date
—
After the change.

Usage Tip

Great for deadlines: add 30, 60, or 90 days to a start date to find the due date and the weekday it lands on.

THE MATH
Result = start date shifted by the chosen amount and unit
Month and year shifts keep the same day number where possible
This adds or subtracts a number of days, weeks, months, or years from a date.
Month and year shifts keep the same day of the month, adjusting when the target month is shorter.
Day and week shifts are exact day counts.
Month and year shifts follow standard calendar arithmetic.
Choose Subtract to go backward in time from the start date.
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The calculators and tools on Formula Factory are provided for general guidance and informational purposes only. Results are estimates based on standard formulas and the values you enter — they do not constitute professional engineering, electrical, or architectural advice. Always verify calculations with a qualified professional before making decisions for any safety-critical, code-compliance, or commercial application. Formula Factory makes no representations or warranties as to the accuracy or completeness of any result, and accepts no liability for errors, omissions, or any outcomes arising from reliance on this information.