How Many Weeks Between Two Dates? – Calculator & Guide

Few date calculations are as deceptively simple as counting weeks between two dates. A quick mental math of “divide days by 7” seems easy, but the details—how to handle partial weeks, which days count, and whether you’re using calendar weeks or work weeks—can trip up even seasoned planners. This guide walks through manual methods, Excel formulas, and online week calculators so you can get the right answer every time.

Days in a week: 7 ·
Weeks in a year (average): 52.1775 ·
Days in a year (average): 365.25 ·
Excel date calculation function: DATEDIF

Five key facts at a glance: the bedrock data points behind every weeks-between-dates calculation.

How many weeks are between two dates?

• Divide the total number of days by 7 to get decimal weeks (Inch Calculator)
• Round down for full weeks, keep remainder for weeks+days (PlanetCalc)
• Manual method: subtract start date from end date using calendar days (Inch Calculator)

The simplest answer: count the days between the two dates and divide by 7. For example, from March 1 to March 22, there are 21 days, which is exactly 3 weeks. If the days aren’t evenly divisible by 7, you get a decimal—say 2.43 weeks—or you can express it as “2 weeks and 3 days.”

Doing this manually means listing the start and end dates, counting the remaining days in the start month, adding the days in full intervening months, and then the days in the end month. Sum everything and divide by 7.

The implication: for accuracy and speed, a calculator or spreadsheet is often the better choice for ranges spanning multiple months.

How to calculate the number of weeks between two dates in Excel?

• Use =DATEDIF(start_date, end_date, "d")/7 for decimal weeks (Microsoft Support)
• Use =INT(DAYS(end_date, start_date)/7) for full weeks only (TrumpExcel)
• Alternatively, =WEEKNUM(end_date) – WEEKNUM(start_date) gives week-number difference
• Google Sheets: =DATEDIF(A1, B1, "D")/7 with ROUNDDOWN for whole weeks

Excel makes this trivial. The DATEDIF function (officially documented by Microsoft Support) computes days, and dividing by 7 converts to weeks. Remember to format the result cell as a number to see decimals. For completed weeks only, the INT function chops off the fractional part.

If you need work weeks—excluding weekends—use =NETWORKDAYS.INTL(start_date, end_date) and then divide by 5. Microsoft Support recommends NETWORKDAYS.INTL for excluding holidays as well.

“The DATEDIF function returns the number of days between two dates; dividing by 7 converts days to weeks.”

— Microsoft Support documentation

The pattern: Excel’s functions give you precise control over how weeks are counted, from basic day division to business-day exclusions.

How to use a week calculator from a date?

• Enter start and end dates to get weeks and leftover days (Inch Calculator)
• Most calculators also display months, years, and total days (PlanetCalc)
• Make sure the date format matches the calculator’s settings (MM/DD/YYYY vs DD/MM/YYYY)

Online week calculators save time. Typing “weeks between dates calculator” into a search engine brings up dozens of free tools. They usually let you pick two calendar dates and output the result in weeks–days or decimal weeks. Many also show the total number of days and months, which adds context.

For instance, Inch Calculator provides a clean interface where you set the start and end fields and get an instant result. PlanetCalc shows both decimal and whole-weeks-plus-remainder views.

What this means: always verify the calculator’s week-start convention to avoid misalignment with your reporting period.

How many weeks calculator for pregnancy?

• Pregnancy weeks are counted from the first day of the last menstrual period (LMP) (Inch Calculator)
• Gestational age differs from fetal age (conception occurs ~2 weeks after LMP)
• Online pregnancy calculators output due date, current week, and trimester

Pregnancy week calculators are among the most popular “weeks between dates” tools. They use the LMP as the starting point and assume a 40-week gestation. Enter the LMP date, and the calculator tells you how many weeks pregnant you are, along with the estimated due date and trimester milestones.

Some calculators also accept a due date to work backwards. Because conception happens roughly two weeks after LMP, “gestational age” and “fetal age” are not the same—a point that often confuses first‑time parents.

“Counting weeks from the last menstrual period is the standard medical practice for determining gestational age.”

— Medical consensus (cited by pregnancy calculators)

The catch: using the wrong starting point can misalign your due date estimate by two weeks, so confirm the calculator’s method before sharing results with your provider.

How to add weeks to a date?

• Add weeks × 7 days to the start date (Inch Calculator)
• In Excel, =A1 + (weeks*7) works directly
• Online calculators have an “add weeks” mode that does the arithmetic for you

Adding weeks is the reverse of finding the difference. Manually, multiply the number of weeks by 7 and add those days to the start date. In Excel, a simple formula like =B2 + (C2*7) works because Excel stores dates as serial numbers. For example, adding 4 weeks to March 1 yields March 29.

Online “add weeks to a date” calculators let you type the start date and the number of weeks, and they return the new date. Many also show the day of the week and handle month‑year rollovers automatically.

Step-by-step: How to calculate weeks between dates manually

1. Identify the start date and end date. Write them down in day-month-year format.
2. Count remaining days in the start month. Subtract the day number of the start date from the total days in that month.
3. Add full months in between. For each complete month between start and end, add that month’s days.
4. Add days from the end month. Use the day number of the end date as the final portion.
5. Divide total days by 7. The quotient is full weeks; the remainder is leftover days.

This manual approach mirrors what a spreadsheet does internally. It’s useful when you don’t have access to a computer, but for anything more than a few months, a calculator or Excel is far less error‑prone.

Related reading: How Many Days Till Easter? Countdown

For those tracking a pregnancy, a pregnancy week calculator can help you determine exactly how many weeks along you are.

Frequently asked questions