Add or Subtract Days from a Date Add or subtract days, weeks, months, or years from any date.

📅

Add or Subtract Days

Add or subtract days, weeks, months, or years from any date.

Select Base Date

Choose your starting date using the date picker.

Choose Operation

Select whether to add or subtract, enter the amount, and choose the unit.

See Result

View the resulting date with full formatting including day of week.

Loading tool...

What Is Add or Subtract Days?

The Add or Subtract Days calculator lets you quickly find a future or past date by adding or subtracting a specified number of days, weeks, months, or years from any starting date. This is invaluable for calculating deadlines, expiration dates, due dates, or any scenario where you need to project forward or backward in time. The tool handles all calendar complexities including leap years, varying month lengths, and end-of-month edge cases. Results show the full formatted date, ISO format, day of the week, and the total number of days between the original and resulting date. It runs entirely in your browser for instant, private calculations.

Why Use Add or Subtract Days?

Supports four time units: days, weeks, months, and years
Toggle between add and subtract with a single click
Shows results in multiple formats including ISO and full date
Handles month-end edge cases (e.g., adding 1 month to January 31)
Instant results with no page reload or server requests
Clean, mobile-friendly interface with large touch targets

Common Use Cases

Payment Due Dates

Calculate when a payment is due 30, 60, or 90 days from the invoice date.

Warranty Expiration

Find the expiration date of a warranty by adding years or months to the purchase date.

Prescription Refills

Calculate when a 90-day prescription needs to be refilled.

Project Milestones

Set milestone dates by adding weeks or months to the project start date.

Travel Planning

Find the return date by adding the number of trip days to the departure date.

Technical Guide

This tool uses JavaScript's native Date methods (setDate, setMonth, setFullYear) for date arithmetic. When adding months, the JavaScript Date object automatically handles overflow — for example, adding 1 month to January 31 results in March 3 (or February 28/29 in the underlying engine, then rolls over). The tool parses the base date at midnight local time to avoid timezone-related off-by-one errors. The subtraction operation simply multiplies the amount by -1 before applying the same addition logic. The ISO date output uses the toISOString() method split at "T" for the date portion, while the formatted output uses toLocaleDateString() with the "en-US" locale for consistent formatting. The day-of-week calculation is derived from the JavaScript Date object's built-in getDay() method, formatted via the Intl.DateTimeFormat API.

Tips & Best Practices

1
Use "weeks" for project sprint planning (e.g., add 2 weeks)
2
Adding months handles end-of-month correctly but may roll over — always verify
3
The ISO date format (YYYY-MM-DD) is ideal for database entry and API calls
4
Use subtract to find retroactive dates like 90 days before today
5
Combine with the Date Difference Calculator to verify results

Related Tools

Date Difference Calculator

Calculate the exact number of days, months, and years between any two dates.

📅 Date & Time

Business Days Calculator

Calculate the number of business (working) days between two dates, excluding weekends.

📅 Date & Time

Relative Time Calculator

Show how long ago or how far in the future any date/time is, with live updating.

📅 Date & Time

Date Range Generator

Generate a list of dates within a range with configurable step and format options.

📅 Date & Time

Recurring Date Calculator

Calculate dates for recurring events at daily, weekly, monthly, or yearly intervals.

📅 Date & Time

Frequently Asked Questions

Q What happens when adding 1 month to January 31?

JavaScript rolls the date forward, resulting in March 2 or 3 depending on whether it's a leap year. This matches how most calendar applications handle month addition.

Q Can I add fractional days?

The tool accepts whole numbers only. For sub-day calculations, use the Time Duration Calculator instead.

Q Does it handle Daylight Saving Time changes?

Yes, dates are calculated at midnight and use calendar days, so DST transitions don't cause off-by-one errors.

Q What's the maximum amount I can add?

There's no practical limit. You can add thousands of years in any direction within JavaScript's Date range.

Q Is the result in my local timezone?

Yes, all calculations use your browser's local timezone for consistent results.

About This Tool

Add or Subtract Days is a free online tool by FreeToolkit.ai. All processing happens directly in your browser — your data never leaves your device. No registration or installation required.