Pick a start date, a number and what to add – days, weekdays, weeks, months or years – and the calculator gives the resulting date and its weekday. Use a minus sign to go back in time. Today is the default start date, set to your own calendar day.
From January 1, 2027
| Add | Result |
|---|---|
| 30 days | Sunday, January 31, 2027 |
| 60 days | Tuesday, March 2, 2027 |
| 90 days | Thursday, April 1, 2027 |
| 100 days | Sunday, April 11, 2027 |
| 180 days | Wednesday, June 30, 2027 |
| 365 days | Saturday, January 1, 2028 |
| 6 months | Thursday, July 1, 2027 |
| 1 year | Saturday, January 1, 2028 |
Adding a whole number of weeks never changes the weekday: 7, 14 or 70 days from a Monday is always a Monday.
Months and the end of the month
Adding months keeps the same day of the month when it exists. When it does not, the result is the last day of the shorter month:
- January 31 + 1 month = February 28 (February 29 in a leap year)
- March 31 + 1 month = April 30
- August 31 − 6 months = February 28
This is how contracts, subscriptions and anniversaries are usually counted. Adding 30 days instead can land on a different date: 30 days after January 31 is March 2 in a common year.
Weekdays (business days)
Choosing “Weekdays” skips Saturdays and Sundays. 10 weekdays from a Monday is the Monday two weeks later; 1 weekday from a Friday is the next Monday. Public holidays are not skipped, because they depend on the country: for a deadline counted in working days, add one day for each holiday in between.
Common uses
- 90-day periods: returns, warranties, probation periods and many visa rules count 90 days.
- Deadlines in working days: offers, payment terms and notice periods.
- Planning: “100 days until…” countdowns, project milestones and follow-up dates.
Check legal deadlines against the rules that apply to you: some count the start day, some do not, and some move a deadline that falls on a weekend to the next weekday. Once zet4u is saved on your phone, the calculator keeps counting with no internet – on a train, a plane or abroad (how it works offline).
Frequently asked questions
How do I add days to a date?
Count forward from the start date. 90 days after January 1, 2027 is April 1, 2027. The calculator counts the real calendar, including month lengths and leap years.
What is the difference between adding 3 months and adding 90 days?
Months follow the calendar, days do not. Three months after January 1 is always April 1. Ninety days after January 1 is April 1 in a common year, but March 31 in a leap year, because February has an extra day.
How do I add business days?
Choose 'Weekdays'. The calculator skips Saturdays and Sundays. Public holidays differ by country, so add one day for each holiday that falls in your period.
How do I count backwards?
Type a negative number. −30 days from March 1, 2027 is January 30, 2027.
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