The Date Calculator adds or subtracts days, weeks, months or years from a start date and tells you the resulting date and weekday. Use it to find a due date 90 days from today, the expiry of a 6-month warranty, the last day of a notice period, a follow-up appointment 12 weeks away, the date 45 days before an event, or when a 3-year policy matures.
How to use the date calculator
- Start date: this is filled with today. Change it to any date.
- Operation: Add (+) for a future date or Subtract (−) for a past one.
- Amount and unit: days, weeks, months or years.
- Press Calculate Date to see the resulting weekday, the full date and the ISO format (YYYY-MM-DD).
How each unit is added
- Days: counts calendar days, including weekends and holidays. 2 November 2026 + 90 days = Sunday, 31 January 2027.
- Weeks: 7 days per week. 2 November 2026 + 12 weeks = Monday, 25 January 2027. The weekday always stays the same.
- Months: moves to the same day number in the target month. 15 March + 2 months = 15 May.
- Years: moves to the same date in the target year.
Month-end rule
If the start day doesn’t exist in the target month, the result is the last day of that month. 31 January + 1 month = 28 February (29 in a leap year), not 3 March. 29 February 2024 + 1 year = 28 February 2025. Banks, insurers and most legal documents count “one month” this way. Some spreadsheet functions behave differently, so if you need a strict day count, use the days unit instead.
Days vs months: they are not the same
“90 days” and “3 months” can end on different dates because months have 28 to 31 days. From 2 November 2026:
| Added | Result |
|---|---|
| + 90 days | Sun, 31 January 2027 |
| + 3 months | Tue, 2 February 2027 |
| + 13 weeks (91 days) | Mon, 1 February 2027 |
Contracts, visas and medical instructions usually say exactly which they mean. If it says “within 30 days”, count days, not one month.
Common uses
| Situation | What to enter |
|---|---|
| Notice period (e.g. 60 or 90 days) | Resignation date + 60/90 days |
| Product return window | Delivery date + 7/10/30 days |
| Warranty expiry | Invoice date + 1 or 2 years |
| Loan or FD maturity | Start date + tenure in months |
| Pregnancy due date (Naegele’s rule) | First day of last period + 280 days (40 weeks) |
| Medicine course or follow-up visit | Today + prescribed days or weeks |
| Countdown planning (“start 45 days before”) | Event date − 45 days |
| Passport or visa validity check | Travel date + 6 months, then compare with the expiry |
Counting manually
To add days by hand, fill up the rest of the current month first, then move through whole months. For 2 November + 90 days: November has 28 days left (to the 30th), leaving 62. December uses 31, leaving 31. January uses 31, leaving 0, so the answer is 31 January. Remember the month lengths with the knuckle trick: knuckles are the 31-day months.
Day of the year
Some forms and industries use the day number within the year (1–365, or 366 in a leap year), called the ordinal date. 2 November 2026 is day 306 of the year. The ISO format shown in the results (YYYY-MM-DD) is the international standard. It sorts correctly in spreadsheets and avoids confusion between Indian (DD/MM) and US (MM/DD) date styles.
Related tools
To skip weekends, use the Business Days Calculator. To count the time between two dates, use the Date Difference Calculator.
Frequently asked questions
What date is 90 days from today?
Enter today’s date, choose Add, type 90 and choose Days. For example, 90 days after 2 November 2026 is Sunday, 31 January 2027.
Does the date calculator include weekends?
Yes. Days are calendar days, including weekends and holidays. To count only weekdays, use the Business Days Calculator.
What is 31 January plus one month?
The calculator returns the last day of February: 28 February, or 29 February in a leap year. This end-of-month rule matches how banks and contracts usually count months.
How do I calculate a date in the past?
Choose Subtract (−) as the operation. For example, subtract 45 days from an event date to find when to start preparations.
Is 3 months the same as 90 days?
Not exactly. Three calendar months can be 89 to 92 days depending on which months are involved. Use the unit your document specifies.