How to Add Days to a Date

When you need to add days to a date

This calculation comes up constantly. You sign a 30-day free trial and want to know the exact date it expires. A contractor gives you a 14-day window to review a proposal. A prescription runs out in 90 days. Your passport requires 6 months of validity beyond your travel date. In every case, you need a reliable way to count forward from a known starting point.

Adding days sounds easy until a month boundary gets in the way. January has 31 days. February has 28 (or 29). March has 31. The calendar is deliberately irregular, which means you cannot just multiply and expect the right answer.

Three methods for adding days to a date

Method 1: Use an online date calculator

The date calculator on this site handles this in seconds. Select the "Add or subtract days" mode, enter your starting date, type in the number of days, and the landing date appears immediately. This is the right choice for one-off lookups and for any span that crosses a month or year boundary.

Method 2: Use a spreadsheet

If your starting date is in cell A1 and the number of days is in B1, type =A1+B1 in another cell and format it as a date. Excel and Google Sheets store dates as integers under the hood, so adding a plain number works correctly. This approach shines when you need the same calculation across hundreds of rows.

Method 3: Count manually

For short spans (say, under two weeks), a paper or digital calendar works fine. Start on your date, count forward one day at a time, and note where you land. For anything longer, errors creep in at month boundaries.

Worked examples

Solid examples beat theory. Here are eight scenarios, including some that cross tricky month and year boundaries.

The January 31 example is the one that catches people. Add 30 days to January 31 and you expect to land on February 28 or thereabouts. But February ends on day 28 (in 2026), so 1 day runs into March, then 2 more fill out to March 2. Leap years shift that result by a day.

What date is 90 days from today?

This is one of the most searched date questions online. From June 21, 2026, adding 90 days lands on September 19, 2026. The count goes: 9 days left in June (June 21 to June 30), then all 31 days of July (running total: 40), then all 31 days of August (running total: 71), then 19 days into September (total: 90). Result: September 19.

The same logic applies to any "X days from today" question. Use the date calculator to automate it for any starting date.

How many days is 2 weeks?

Two weeks is exactly 14 days, always. One week is 7 days regardless of which month or year it falls in. Multiples of 7 are the one date arithmetic constant you can always rely on.

Adding days that cross a year boundary

Adding days across December 31 into January works the same way as any other month crossing. From December 1, 2026, adding 45 days: 30 days remain in December, so you carry 15 into January 2027, landing on January 15, 2027. No special rule applies at year end.

Related guides

If you need to go the other direction, see how to subtract days from a date. For counting just working days in your result, see business days vs. calendar days explained.