To calculate weeks between two dates, count the total days between them and divide by 7. The whole number is the count of complete weeks, and the remainder is the number of leftover days. For example, 30 days equals 4 full weeks and 2 days, which is 4.29 weeks as a decimal.

Once you know the day count, the rest of the math takes seconds. This guide shows the steps, worked examples with real dates, and the small details that change the answer.

What Is the Basic Formula for Weeks Between Two Dates?

The formula has two parts: find the number of days, then convert days to weeks.

1. Days between dates = end date minus start date
2. Weeks between dates = days between dates divided by 7

Write the result two ways. As whole weeks plus leftover days (for example, 10 weeks and 6 days), which is easy to picture on a calendar. Or as a decimal number of weeks (for example, 10.86 weeks), which suits project plans and spreadsheets.

How Do You Count the Days Between Two Dates?

The day count is where most mistakes happen. Follow these steps in order.

Step 1: Decide whether to include the start date

Most calendar math uses exclusive counting: the start date is day zero, and each date after it adds one day. Under this method, the days between Monday and the following Monday is exactly 7.

Inclusive counting counts both the start and end dates, adding one extra day. Use exclusive counting unless you have a reason to do otherwise.

Step 2: Count days month by month

Work from the start date to the end date, adding the days in each month you pass through. Standard month lengths: January 31, February 28 (29 in a leap year), March 31, April 30, May 31, June 30, July 31, August 31, September 30, October 31, November 30, December 31.

Step 3: Add the partial months at each end

For the starting month, subtract the start day from the month’s total days. For the ending month, use the end day directly. Add both partial months plus all full months in between.

Step 4: Double-check with a day-of-week test

If the two dates fall on the same day of the week, the day count must be a multiple of 7. If it is not, you made an arithmetic error.

How Do You Convert Days to Weeks?

Divide the day count by 7. The whole-number part is complete weeks, and the remainder is leftover days.

• Complete weeks = days divided by 7, rounded down
• Leftover days = days minus (complete weeks times 7)
• Decimal weeks = days divided by 7, kept as a decimal

This table shows how common day counts convert:

Days between dates	Complete weeks	Leftover days	Decimal weeks
7	1	0	1.00
14	2	0	2.00
30	4	2	4.29
45	6	3	6.43
60	8	4	8.57
90	12	6	12.86
100	14	2	14.29
180	25	5	25.71
365	52	1	52.14
366	52	2	52.29

Notice the last two rows: a standard year is 52 weeks and 1 day, and a leap year is 52 weeks and 2 days. That is why there are not exactly 52 weeks in a year, even though people often round it that way.

What Are Some Worked Examples?

Here are three examples calculated step by step with real dates.

Example 1: October 17, 2026 to January 1, 2027

1. October 17 to October 31: 31 minus 17 = 14 days
2. November: 30 days
3. December: 31 days
4. January 1: 1 day
5. Total: 14 + 30 + 31 + 1 = 76 days
6. 76 divided by 7 = 10 weeks with a remainder of 6 days (10 times 7 = 70, and 76 minus 70 = 6)

Answer: 10 weeks and 6 days, or 10.86 weeks.

Example 2: June 1, 2026 to December 25, 2026

1. June 1 to June 30: 30 minus 1 = 29 days
2. July through November: 31 + 31 + 30 + 31 + 30 = 153 days
3. December 25: 25 days
4. Total: 29 + 31 + 31 + 30 + 31 + 30 + 25 = 207 days
5. 207 divided by 7 = 29 weeks with a remainder of 4 days (29 times 7 = 203, and 207 minus 203 = 4)

Answer: 29 weeks and 4 days, or 29.57 weeks.

Example 3: January 1, 2026 to December 31, 2026

1. 2026 is not a leap year, so the year has 365 days
2. December 31 minus January 1 (exclusive count) = 364 days
3. 364 divided by 7 = 52 weeks with no remainder

Answer: exactly 52 weeks. Both January 1 and December 31, 2026 fall on a Thursday, which confirms the multiple-of-7 rule. Counting inclusively (both endpoints) would give 365 days, or 52 weeks and 1 day.

Should You Count the Start Date, the End Date, or Both?

This choice changes the answer by exactly one day, which can matter for contracts and deadlines. State your method so everyone works from the same number.

• Exclusive (recommended): start date counts as day zero. Monday to the next Monday is 7 days, exactly 1 week. Use this for durations, countdowns, and planning.
• Inclusive: both endpoints count. Monday to the next Monday is 8 days. Use this only when someone asks “how many calendar days does this span,” such as a hotel stay quoted per night.

When in doubt, state your method. Writing “76 days (exclusive of the start date)” removes all confusion.

How Do Leap Years Affect the Calculation?

A leap year adds February 29, which adds one extra day to any date range that includes that date. If your range starts and ends on the same side of February 29, the leap year changes nothing.

For example, the range from March 1, 2028 to February 28, 2029 crosses February 29, 2028, so it holds 366 days instead of 365: 52 weeks and 2 days rather than 52 weeks and 1 day.

What Tools Can Do This Math for You?

• Spreadsheet formulas: in Excel or Google Sheets, =B1-A1 gives days between two dates, and =(B1-A1)/7 gives decimal weeks.
• Online date calculators: search “days between dates” for calculators that handle month lengths and leap years automatically.
• Phone calendar apps: most let you jump to a future date and read the day count from the date picker.
• Python: (date(2027,1,1) – date(2026,10,17)).days returns 76 directly.

Even with a tool, the manual method helps you catch mistakes, such as an inclusive-count setting that quietly adds a day.

Frequently Asked Questions

How many weeks are between January 1 and December 31 of the same year?

Exactly 52 weeks, counting exclusively, because the span is 364 days. Counting inclusively, it is 52 weeks and 1 day in a standard year or 52 weeks and 2 days in a leap year.

What is the fastest way to calculate weeks between two dates?

Subtract the start date from the end date to get total days, then divide by 7. In a spreadsheet, =(B1-A1)/7 does both steps at once.

Do I count the start date when calculating weeks between dates?

Usually no. The standard method treats the start date as day zero, so Monday to the following Monday is exactly 7 days.

How do leap years change the weeks between two dates?

A leap year adds one day (February 29) to any range that includes it, which can turn a remainder of 1 leftover day into 2. Ranges that stay on one side of February 29 are unaffected.

How do I express a remainder, like 76 days, in weeks?

Divide by 7 and split the result: 76 days is 10 complete weeks (70 days) plus 6 leftover days, or 10.86 weeks as a decimal.

Understanding how weeks fit between dates also helps with the bigger picture of weeks in a year. If you are working with a fixed day count instead, see our guide on how many weeks are in 100 days. You can also reach us through our about us page if you have a date-math question we did not cover.