Add Weeks to Date Calculator
Add or subtract weeks (plus extra days) from any date: see the exact date and weekday, the total days, a week-by-week list, and an optional move to the next working day that skips weekends and US, Mexican, Colombian or Spanish holidays.
How it works
result = start date ± (weeks × 7 + extra days) calendar days · optional: move a weekend or holiday result to the next or previous working day
Adding whole weeks always lands on the same weekday, because seven days is exactly one week: start on a Tuesday and you finish on a Tuesday. The calculator multiplies the weeks by 7, adds any extra days, and moves the date that many calendar days, so month ends, year ends and February 29 are all handled. Switch the direction to count backward, for example to find the date 12 weeks before an exam. The week-by-week list shows every week’s date along the way, which is handy for course plans, training blocks, pregnancy weeks or recurring appointments. Under More options you can flag weekends and public holidays (US federal, Mexico’s official rest days, Colombia’s national holidays with their Monday moves, or Spain’s national holidays), move a result that falls on a day off to the next or previous working day, and repeat the offset to build a schedule such as every 4 weeks.
Worked example
Six weeks after Tuesday, September 15, 2026 is 6 × 7 = 42 days later: Tuesday, October 27, 2026, still a Tuesday, in ISO week 44 and the 300th day of the year. Twelve weeks and 3 days after Monday, June 1, 2026 is 84 + 3 = 87 days later: Thursday, August 27, 2026. With US federal holidays and “move to the next working day” on, 15 weeks after Saturday, September 12, 2026 would be Saturday, December 26, 2026, which moves to Monday, December 28, 2026.
Sources: OPM — Federal holidays · Mexico — Federal Labor Law, Article 74 · Colombia — Law 51 of 1983 (holidays)
Frequently asked questions
Will the result always be the same weekday?
Yes, as long as you add whole weeks and no extra days. A week is exactly seven days, so any whole number of weeks lands on the same weekday. Extra days or a move to a working day can change it.
How many days are in a given number of weeks?
Multiply by 7: 4 weeks is 28 days, 6 weeks is 42, 12 weeks is 84, 20 weeks is 140 and 52 weeks is 364, one day short of a common year.
Are leap days handled?
Yes. The calculator counts real calendar days, so a span that crosses February 29 still moves by exactly weeks × 7 days.
What does “last day if the start date is day 1” mean?
If a 6-week leave, course or prescription starts on a Monday and counts that Monday as day 1, its last day is the Sunday six weeks later, one day before the plain result. The plain result is the day after the period ends.
Can it skip weekends and holidays?
Weeks are always calendar weeks, but under More options you can mark the result as a working day or not and move a weekend or holiday result to the next or previous working day, using US, Mexican, Colombian or Spanish national holidays.
How is this different from adding months?
Weeks are a fixed 7-day step, so the weekday is kept but the day of the month drifts. Months keep the day of the month but vary in length, so use a date add or subtract calculator for month-based terms.
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This calculator is for educational purposes. Double-check important results before acting on them.