Date Add & Subtract Calculator
Add or subtract days, weeks, months and years from a start date, with leap year and month-end handling
Operation
Time Amount
Quick Presets
All calculations run locally
All date calculations are performed in your browser. No data is uploaded to any server.
Results are based on the Gregorian calendar and selected counting rules. For contracts, payments, legal, medical or other important deadlines, please verify with relevant documents, local regulations and professional advice.
About Date Add & Subtract Calculator
This tool helps you calculate a new date by adding or subtracting years, months, weeks and days from a start date. It automatically handles leap years, different month lengths and month-end dates.
How to Use
- Select a start date using the date picker or quick shortcuts
- Choose whether to add or subtract
- Enter the number of years, months, weeks and/or days
- View the result date and calculation steps
- Copy the result or use it as a new start date
Date Add/Subtract vs Date Difference
Date Add/Subtract calculates a new date from a start date by adding or subtracting time. Date Difference calculates the time between two dates. This tool is for the first use case.
Calculation Rules
When you enter multiple units, calculations are performed in this order: years first, then months, then weeks (converted to days), then days. This ensures consistent results across all scenarios.
Month-End Date Handling
If the target month doesn't have the corresponding day (e.g., January 31 + 1 month), the result is adjusted to the last day of the target month (February 28 or 29). This is the most intuitive behavior for most users.
Leap Year Handling
Leap years follow Gregorian calendar rules: divisible by 4 (except centuries not divisible by 400). February 29 + 1 year = February 28 of the next year. February 29 + 4 years = February 29 of the target leap year.
Include Start Date Option
The 'Include Start Date' option only affects day and week counting. For example, starting October 1 and adding 1 day: without including = October 2; with including = October 1. This option does not affect month or year calculations.
Calculation Order
When multiple units are entered, calculations follow a fixed order: years → months → weeks → days. Each step uses the result of the previous step as its starting point.
Common Use Cases
- Calculate contract expiration dates
- Calculate probation period end dates
- Calculate project deadlines
- Calculate warranty expiration dates
- Calculate subscription renewal dates
- Calculate travel dates
- Calculate medical appointment dates
- Calculate event dates
- Calculate payment due dates
- Calculate future or past anniversary dates
Data & Privacy
All date calculations are performed locally in your browser. No date data is sent to any server or recorded in analytics.
Limitations
- Only supports Gregorian calendar dates (year 1 to 9999)
- Does not handle time zones or daylight saving time
- Does not account for holidays or special calendar systems
- Month-end adjustment always uses the 'clamp to last day' rule