Add or Subtract Days from a Date

When you need date arithmetic

• Deadlines: “submit within 30 days of receiving the notice”.
• Validity: a document valid for 6 months from the issue date.
• Notice periods: 60 or 90 days from your resignation date.
• Loans and payments: due dates, grace periods and EMI start dates.
• Health: 45 days after a vaccination or medicine course.
• Going back: “what date was 100 days ago?”

Days vs months

Adding days and weeks is exact: 30 days after 15 January is 14 February. Adding months moves the calendar month and keeps the day number where possible; if the day doesn’t exist in the target month, the last day of that month is used. For example, 31 January + 1 month = 28 February (or 29 in a leap year). This matches how most contracts and legal periods count months.

Weekday included

The result shows the full date with its weekday, so you can instantly see whether a deadline falls on a Sunday.

Legal and official periods

Some laws and rules define periods differently, such as “excluding the first day” or “clear days”, or extending to the next working day if the deadline falls on a holiday. Check the specific rule, and adjust by a day if needed.

Related

For business days only, use the working days calculator. To count the gap between two dates, use the date difference calculator. For the weekday of any date, try the day finder.

Examples

• Rent agreement of 11 months from 1 April ends on 1 March the next year; the day before is the last day of the term.
• A 45-day return window from 20 September ends on 4 November.
• A document valid for 6 months from 31 August expires on 28 February (or 29 in a leap year).
• 100 days before 26 January 2027 was 18 October 2026.