How this calculator works
- Step 1Start4 Nov 2026Pick the date to count from.
- Step 2Months firstyears, monthsMove whole calendar months, keeping the day if it exists.
- Step 3Then daysweeks, daysCount calendar days forward or back.
The calculator moves years and months on the calendar first, then counts weeks and days. Every day counts, including weekends and holidays.
Worked example: a mixed period
- Order
years and months, then weeks and days
- Start4 Nov 2026
- + 1 year 2 months14 calendar months4 Jan 2028
- + 3 weeks 4 days25 days29 Jan 2028
- Result451 days laterSaturday, 29 Jan 2028
90 days after the same start is 2 Feb 2027, a Tuesday.
The month-end rule
- 31 Jan + 1 month28 Feb 2026February has no 31st, so its last day is used.
- 31 Jan + 30 days2 Mar 2026Counting days lands in March instead.
“One month” and “30 days” are different periods; pick the one your deadline uses.
Read the result
Counting back works the same way: 280 days before 4 Nov 2026 is 28 Jan 2026. The result shows its weekday, so you can check whether a deadline falls on a weekend.
Assumptions and limits
- Calendar daysWeekends and holidays are counted.
- Leap yearsGregorian rules, 1900 to 2100.
- Month endA missing day moves to the month’s last day.
- No timesWhole dates only; no hours or time zones.
Related date tools
Moving a date is the reverse of counting between dates.
To count the gap between two dates, use the date difference calculator. For business days only, try the working days calculator, and for a weekday, the day of the week calculator.
Common mistakes
Mistake: Treating 3 months as 90 days.
Instead: Enter months, or days, as your rule states.
Mistake: Counting working days with this tool.
Instead: Use the Working Days Calculator.
Mistake: Assuming the start day is counted.
Instead: Day 1 is the day after the start date.
Checking the method
A separate script re-works every golden value with Python's own date library instead of day numbers.
Read how we test our calculators, or browse more everyday tools.