Weeks Between Dates Calculator

Whole weeks first, leftover days second

Every weeks-between-dates answer starts as a day count. You find the whole days between the two dates, divide by 7, and read the answer in two parts: whole weeks, then leftover days. From October 25, 2026 to December 20, 2026 the day count is 56, and 56 / 7 = 8 weeks with nothing left over. From October 25 to November 27 the day count is 33, which is 4 weeks plus 5 days, because 4 x 7 = 28 and 33 - 28 = 5.

The remainder matters. "8 weeks apart" and "8 weeks 5 days apart" are different plans for rent due dates, project sprints, pay periods and notice periods. A sprint calendar that assumes clean weeks drifts by the remainder, and the drift compounds if you stack spans back to back.

This page counts the start date but not the end date, which is the convention most calendars use. Type a start and an end date in the widget above and it returns the day count, the weeks and days split, the inclusive count, the weekday split and the ISO week numbers on each end. There is also a reverse box for the other direction: pick a target date, type a number of weeks, and get the date that many weeks back.

Worked example: October 25, 2026 to December 20, 2026

Take the span from Sunday, October 25, 2026 to Sunday, December 20, 2026. Work the day count month by month.

• October 25 to October 31: 31 - 25 = 6 days
• All of November: 30 days
• December 1 to December 20: 20 days

6 + 30 + 20 = 56 days. Divide by 7: 56 / 7 = 8 with a remainder of 0, and 8 x 7 = 56 confirms it. The span is 8 weeks exactly. Notice both endpoints land on a Sunday, which is what a zero remainder means: the end date falls on the same weekday as the start date.

Now a span with a remainder. October 25 to November 27, 2026: 6 days left in October plus 27 in November gives 6 + 27 = 33 days. Divide by 7: 4 x 7 = 28, and 33 - 28 = 5, so the answer is 4 weeks and 5 days. November 27, 2026 is a Friday, five weekdays after the Sunday you started on. The remainder in days always matches the weekday gap: 4 weeks 5 days after a Sunday is a Friday, always.

Do the endpoints count? Exclusive versus inclusive

Counting rules differ by one day depending on whether the end date itself is included. The default on this page is exclusive: the count runs from the start date up to but not including the end date. October 25 to December 20 is 56 days on that reading. Count both endpoints and the same pair is 57 days, because 56 + 1 = 57.

The same one day shows up in tiny spans. Monday to Tuesday is 1 day exclusive and 2 days inclusive. The same date on both ends is 0 days exclusive and 1 day inclusive. Neither reading is wrong; contracts, school calendars and booking systems each pick one. The mistake to avoid is mixing them: a lease that runs 8 exclusive weeks plus a move-out day is 57 days of occupancy, and billing that on 56 days shortchanges one day.

If your own count is one higher than the widget, you are counting inclusively. Switch the toggle, or subtract nothing and keep your number; just apply the same rule everywhere.

When the span crosses the ISO week boundary

Calendar weeks and ISO week numbers are different instruments. The ISO 8601 standard, set out in ISO 8601-1:2019, defines a week as Monday through Sunday and numbers the weeks of a year so that week 1 is the week holding the first Thursday of that year. Those rules make some years 53 weeks long.

October 25, 2026 is a Sunday, the last day of ISO week 43. December 20, 2026 is also a Sunday, ending ISO week 51. January 3, 2027 lands on week 53 of 2026, because January 1, 2026 is a Thursday and the year therefore carries 53 ISO weeks. The day count from October 25, 2026 to January 3, 2027 is 6 + 30 + 31 + 3 = 70 days, which is 70 / 7 = 10 weeks exactly.

Here is the trap: week 43 to week 53 looks like 10 weeks if you subtract, but the labels span 11 week numbers counting both ends. Week labels answer "which week is this date in", not "how long is the gap". When a span crosses a year boundary, or crosses one of the 53-week years such as 2026, derive weeks from days, never from week numbers.

Work weeks inside a calendar span

A calendar week holds 5 weekdays and 2 weekend days, so whole weeks make the weekday split easy. The 56 days counted from October 25, 2026 run from Monday, October 26 through Sunday, December 20: exactly 8 Monday-to-Sunday blocks. That is 8 x 5 = 40 weekdays and 8 x 2 = 16 weekend days.

Shift the start and the mix changes even when the total stays put. The table shows the three worked spans on this page, all counted exclusively from October 25, 2026.

For planning work, the weekday count is usually the number that matters. A project quoted at 8 weeks needs 40 working days if the crew works Monday to Friday. Delivery windows, clinic schedules and freelance timelines all live on the 5-day calendar even when the client speaks in weeks. The widget computes the weekday and weekend split for any pair of dates, so you can see the mix before you commit to a date.

Counting backward: the date N weeks before

Weeks run both directions. To find the date N weeks before a target, subtract 7 x N days, and the weekday stays the same because a week is 7 days in every calendar.

• 8 weeks before December 20, 2026: 8 x 7 = 56, and December 20 minus 56 days is October 25, 2026, a Sunday, the same weekday as the target.
• 9 weeks before December 20, 2026: 9 x 7 = 63, which lands on October 18, 2026, also a Sunday.
• 3 weeks before January 3, 2027: 3 x 7 = 21, landing on December 13, 2026.

This is the arithmetic behind most "start by" deadlines. A 40-week pregnancy is counted forward from the last period, 40 x 7 = 280 days, but ultrasound dating often hands you a due date and asks how far along you were at some earlier point, which is the same subtraction in reverse. Lease notice windows work the same way: if 60 days notice is due before a December 20 move-out, the deadline is October 21, and knowing it is 8 weeks and 4 days tells you how much calendar room you have.

One caution: subtracting weeks keeps the weekday but crosses month boundaries with their uneven lengths, so never eyeball it on a calendar grid. October has 31 days, September 30, and the offsets do not line up in neat month-sized chunks. The reverse box in the widget does the day arithmetic for you.

Spans people count in weeks most often

Certain spans come up so often that their day counts are worth memorizing. All of these divide evenly except the last row, which is the reason the calendar year never lands on a whole number of weeks.

That last row explains a lot of calendar drift. A common year is 365 days, and 365 / 7 = 52.14, so a year is 52 weeks plus 1 day; a leap year is 52 weeks plus 2. The U.S. Naval Observatory notes in its Julian Date Converter that 7-day weeks have run without interruption, which is why every one of these divisions lands cleanly. Any date advances one weekday per year, two when a February 29 sits in between, which is why the same week number lands on a different weekday each January. Payroll teams feel this directly: 26 biweekly checks cover 364 days, so every 5 to 6 years a year contains 27 of them.

How this page fits the other date tools

The site already carries a cluster of date tools, and this one overlaps with several, so here is the division of labor.

A quick rule of thumb: if the answer should sound like "weeks and days", stay here. If it should sound like a date ("March 14"), use the add-days or week tool. If it should sound like a contract term ("2 years, 3 months"), the years-between page is the right fit.

Everything runs on dates you type, computed in your browser. Nothing is uploaded or stored.