Date Add/Subtract Calculator

Date Add/Subtract

Add or subtract days, weeks, months, or years.

Results

Summary

Result date
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Date Difference Calculator

Find days and weeks between two dates

Countdown Calculator

Days until (or since) a target date

Quick Jump:How It WorksUse CasesExamplesMonth/Year RulesFAQs

How this calculator works

This date calculator lets you add or subtract a specific number of days, weeks, months, or years from any date. Simply enter your base date, choose the operation (add or subtract), select the unit, and specify the amount.

Days & Weeks

Adding days/weeks is straightforward — move forward or backward by exact calendar days. 7 days = 1 week, always.

Months & Years

Months and years use calendar math. End-of-month dates are safely clamped when the target month has fewer days.

Common use cases

📅 Project Deadlines

Calculate delivery dates by adding business days or weeks to a start date.

💊 Prescription Refills

Know when your 30-day or 90-day supply runs out.

📆 Contract Renewals

Add 1 year (or 6 months) to a contract start date for renewal planning.

✈️ Travel Planning

Calculate return dates or visa expiration dates.

👶 Due Dates

Add 40 weeks to a last menstrual period (LMP) date for pregnancy planning.

📝 Legal Deadlines

Calculate filing deadlines by adding specific days to an event date.

Examples

Jan 31 + 1 month

Result: Feb 28 (or Feb 29 in leap years). Clamped safely to the last day of February.

March 15 - 14 days

Result: March 1. Subtracting days moves backward through the calendar.

Feb 29, 2024 + 1 year

Result: Feb 28, 2025. Since 2025 isn't a leap year, it clamps to Feb 28.

Today + 90 days

Calculates exactly 90 calendar days from today — useful for 90-day planning horizons.

Month and year calculation rules

Unlike days and weeks, months and years have variable lengths. Here's how the calculator handles edge cases:

ScenarioRuleExample
End-of-month clampClamp to last valid dayJan 31 + 1 month → Feb 28
Leap year handlingFeb 29 clamps in non-leap yearsFeb 29 + 1 year → Feb 28
30-day months31st clamps to 30thAug 31 + 1 month → Sep 30

💡 Tip: If you need exact day counts (like 30 or 365 days), use "Days" instead of "Months" or "Years".

Frequently Asked Questions

How does adding months handle end-of-month dates?▼
If the target month has fewer days, the result clamps to the last valid day of that month (e.g., Jan 31 + 1 month → Feb 28/29).
Does this include time of day?▼
No. This tool uses date-only inputs (YYYY-MM-DD) and ignores time of day to avoid timezone/DST issues.
Is adding 30 days the same as adding 1 month?▼
Not always! Months have variable lengths (28-31 days). Adding 30 days always adds exactly 30 days, while adding 1 month moves to the same day of the next month (or clamps if that day doesn't exist).
How do I subtract months or years?▼
Select "Subtract" as the operation and choose "Months" or "Years" as the unit. The same end-of-month clamping rules apply.
What date is 90 days from today?▼
Enter today's date, select "Add", choose "Days", and enter 90. The calculator will show you the exact date and weekday.
Can I calculate a date in the past?▼
Yes! Use the "Subtract" operation to go backward in time. For example, subtracting 30 days from today gives you the date from a month ago.
Does leap year affect the calculation?▼
Yes. When adding months/years, the calculator correctly handles February 29 in leap years. Adding 1 year to Feb 29 results in Feb 28 in non-leap years.
What is the delta days in the result?▼
Delta days shows the exact number of calendar days between your base date and the result date. This helps verify the calculation and is useful for planning.