How do I add or subtract days from a date?
download.fan · Updated
Short answer
Move through the calendar month by month, using up the days as you go. 90 days after November 4, 2026 is February 2, 2027: 26 days finish November, 31 finish December, 31 finish January, and the last 2 land in February. To subtract, count backward the same way: 30 days before November 4, 2026 is October 5, 2026.
Step by step
Step 1: Find the days left in the month
November has 30 days, so November 4 has 26 days left.
Step 2: Take off whole months
90 − 26 = 64. December uses 31, leaving 33. January uses 31, leaving 2.
Step 3: Land on the date
The last 2 days fall in the next month: February 2, 2027.
Step 4: Check for a leap year
If your count crosses February, use 29 days in a leap year such as 2028.
What is the easiest way to add days to a date?
Use a date calculator. Pick a start date, enter the years, months, weeks or days, and choose add or subtract. It can also skip weekends when you turn on business days.
In a spreadsheet, dates are stored as numbers, so =A2+90 adds 90 days and =A2-30 goes back 30. Excel and Google Sheets also have WORKDAY(A2,10) for 10 working days later.
What happens when I add a month to January 31?
February has no 31st, so calendar tools usually move to the last day of February. That means adding one month isn't the same as adding 30 days: January 31 plus 30 days lands in early March, while plus one month gives February 28 or 29.
Read the wording on anything official. "Within 30 days" and "within one month" can give different deadlines.
How do I add business days?
Count only Monday to Friday, and skip public holidays if they apply. As a rule of thumb, 5 business days span 7 calendar days, so 10 business days is usually 14 calendar days. Holidays differ by country and employer, so check them separately for anything with a legal deadline.