Time & Date
Date Calculator
Add or subtract days from a date
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Frequently asked questions
What does the Date Calculator do?
It helps you add or subtract days from a date.
What inputs do I need?
Enter Start date and Days to add.
Are decimals supported?
Yes, you can use decimal values where appropriate.
Related tools
About this tool
Inputs
- Start date
- Days to add
Results
- Result date
- Weekday
Every calculation has variables — and getting even one wrong changes the outcome. The Date Calculator keeps all variables in view so nothing slips through. Start by filling in start date and days to add. Based on these values, the tool computes result date and weekday. Having a dedicated tool to add or subtract days from a date saves time you would otherwise spend searching for formulas or setting up a spreadsheet.
When calculating age or anniversary dates, decide whether to count the start date as day zero or day one. Duration calculations should distinguish between calendar duration (months, years) and exact duration (days, seconds). Days between two dates = |date2 − date1| using Julian Day Numbers avoids month-length complications. The Gregorian calendar adds a leap day every 4 years, except for century years not divisible by 400. Run the calculation with your best-case and worst-case assumptions to bracket the likely outcome.