Date Calculator

A date calculator counts forward or back one calendar day at a time.

Result = start date ± years and months, then ± (weeks × 7 + days)

Pick a start date, choose Add or Subtract, and type the time in any mix of years, months, weeks and days. Weeks and days are plain counts: a week is seven calendar days, and every day counts, weekends and holidays included. Years and months move by the calendar instead, which the section on month ends explains. The start date is day zero, so one day after a Monday is the Tuesday.

The calculator opens on today's date, because so many date questions start from now: 30 days from today for a notice, 90 days from today for a review. The card under the fields lists 30, 60, 90, 180 and 365 days from whatever start date you pick, and the result shows its weekday, its ISO week number and its day of the year, which is what a planning calendar or a payroll system asks for.

Ninety days after Monday, November 2, 2026 is Sunday, January 31, 2027.

Take an invented new hire who starts on Monday, November 2, 2026, with a review planned 90 days later. Type that date, keep Add and enter 90 days.

• November: the start date is not counted, so November 3 to 30 is 28 days.
• December: all 31 days, which brings the count to 59.
• January: all 31 days, which brings it to 90 on January 31, 2027.
• The answer is a Sunday, so the calculator names the next Monday, February 1, 2027.

The breakdown under the result says the same span another way: 90 calendar days is 12 weeks and 6 days, it crosses 64 weekdays, and January 31, 2027 sits in ISO week 4 of 2027 and is day 31 of the year. Running it backwards works too. Switch to Subtract, start from Sunday, January 31, 2027 and take away 60 days, and the answer is Wednesday, December 2, 2026. To check a span you already have both ends of, the days between dates calculator counts it directly.

Ninety days and three months are not the same length.

A quarter can be written three ways, and each lands on a different day. From Monday, November 2, 2026, 12 weeks is 84 days and lands on Monday, January 25, 2027. 90 days lands on Sunday, January 31. Three months lands on Tuesday, February 2, 2027, which is 92 days, because December and January both have 31 days. A six-month mark from the same start is Sunday, May 2, 2027, 181 days later.

Three calendar months run from 89 to 92 days depending on the months, so a rule written in days and a rule written in months give different dates for the same start. Type the period the way the contract, policy or letter writes it: days in the Days field, months in the Months field.

Adding a month keeps the day number unless the month is too short.

One month after January 15, 2027 is February 15, 2027: the day number stays and the month moves on. The question is what happens when the day does not exist in the target month. The calculator uses the month's last day instead, so January 31, 2027 plus one month is February 28, 2027. 2028 is a leap year, so January 31, 2028 plus one month is February 29, 2028. Going back works the same way: March 31, 2026 minus one month is February 28, 2026.

A shortened month does not grow back. February 28, 2027 plus one month is March 28, 2027, not March 31, so two one-month steps from January 31 end three days earlier than a single two-month step, which lands on March 31. When a period is a number of months, add it in one go rather than a month at a time.

Most workplace deadlines in federal rules are counted in calendar days.

Several time limits that HR teams and employees meet are written as a number of days, and the calculator turns each into a date.

• Layoff notice. 20 CFR 639.2 says WARN requires employers planning a plant closing or a mass layoff to give affected employees “at least 60 days' notice.” The WARN notice tracker follows the notices employers file with state labor departments.
• COBRA. 29 U.S.C. 1165 sets an election period for continuing health cover that is “of at least 60 days' duration.”
• FMLA leave. 29 CFR 825.200 limits the entitlement to “a total of 12 workweeks of leave during any 12-month period.” Taken in one block, 12 workweeks run 12 × 7 = 84 calendar days.
• Discrimination charges. The EEOC gives “180 calendar days from the day the discrimination took place,” extended to 300 calendar days where a state or local agency enforces a law against the same kind of discrimination, and adds that “Holidays and weekends are included in the calculation.”

Some deadlines count business days instead. 8 CFR 274a.2 has the employer complete section 2 of Form I-9 “within three business days of the hire,” and a count like that skips weekends and holidays, so it belongs in the business days calculator, which also knows the US federal holidays.

A deadline that lands on a weekend usually moves to the next business day.

The EEOC page puts the rule for its own charges plainly: “if the deadline falls on a weekend or holiday, you will have until the next business day.” Count from the same invented start date, Monday, November 2, 2026, and three of five common spans end on a day most offices are closed.

• 60 days later is Friday, January 1, 2027, New Year's Day, so the next business day is Monday, January 4.
• 90 days later is Sunday, January 31, 2027, so it is Monday, February 1.
• 180 days later is Saturday, May 1, 2027, so it is Monday, May 3.
• 30 days later, Wednesday, December 2, 2026, and 365 days later, Tuesday, November 2, 2027, are ordinary weekdays.

The calculator flags any result that falls on a Saturday or a Sunday and names the Monday after it. Holidays depend on the employer and the rule, so check those against your own calendar, or count the whole period in business days. For a deadline that ends at a clock time rather than a date, the time duration calculator adds hours and minutes across days, the time zone converter shows what that time is in another office, and the military time converter reads a 24-hour time stamp.

The same arithmetic turns notice periods and probation into real dates.

A notice period written as four weeks becomes a last day once you add 28 days to the date it was given, and the resignation letter generator writes that date out in full. A probation period of 90 days becomes a review date the same way. When pay depends on the dates, the hours calculator and the time card calculator add up the hours worked inside them, and the PTO accrual calculator shows how much leave builds up by a given pay period.

A date on the calendar is easier to plan for than a departure nobody saw coming.

A date calculator tells you exactly when a 90-day review falls. It cannot tell you whether the person will still be there for it. By the time a resignation lands, the decision behind it was made weeks earlier, and the notice period is all the time left for a handover. TeamPredict works on the part before that, reading public LinkedIn signals to flag resignation risk early, so the first sign of a departure is a warning while there is still time to talk, rather than a last day already circled on the calendar.