Weeks Between Dates Calculator
Counting weeks between two dates comes up more often than you might expect. Pregnancy is tracked in weeks from the last menstrual period, with a full-term delivery expected at 40 weeks. Workout programs are structured in training weeks, typically 4, 8, or 12 weeks long. Project managers plan in sprints measured in weeks. School terms are counted in weeks, and many financial instruments (such as Treasury bills) mature in fixed week intervals such as 4, 8, 13, 17, 26, or 52 weeks. Calculating weeks manually is simple in principle but easy to get wrong: divide the total number of days by 7 to get complete weeks, and the remainder tells you how many days are left over. This calculator automates that arithmetic, handles month and year boundaries, accounts for leap years, and shows you the total day count alongside the weeks. The start date defaults to today and the end date defaults to 90 days from today, giving a quick three-month view. Change either date to suit your needs. Results update instantly as you type.
How weeks between dates are calculated
The calculator finds the difference between the two dates in whole days, then divides by 7 using integer division (rounding down) to find complete weeks. The remainder after dividing by 7 is the number of leftover days.
totalDays = Math.round((endDate - startDate) / 86400000)
completeWeeks = Math.floor(totalDays / 7)
remainingDays = totalDays % 7
Worked example
Start: 14 June 2026. End: 14 September 2026 (92 days apart).
92 divided by 7 = 13 complete weeks with 1 remaining day. Total: 13 weeks and 1 day.
Common uses for week counts
Pregnancy tracking uses weeks from the last menstrual period. A pregnancy is considered full term at 39 to 40 weeks and post-term after 42 weeks. Fitness programs often run in 4-week mesocycles. Academic semesters commonly run 15 to 18 weeks. Fixed-income instruments like US Treasury bills are issued in standard maturities measured in weeks.
Weeks between dates: frequently asked questions
How are weeks between dates calculated?
The total number of days between the two dates is divided by 7. The whole number part gives complete weeks, and the remainder gives leftover days. For example, 100 days between two dates equals 14 complete weeks and 2 remaining days.
Why do pregnancy weeks matter?
Pregnancy is typically measured in weeks, counting from the first day of the last menstrual period (LMP). A full-term pregnancy is approximately 40 weeks. Knowing the exact week of pregnancy is important for scheduling prenatal appointments, monitoring fetal development, and planning for birth. This calculator can help track pregnancy weeks when you enter the LMP as the start date.
How many weeks are in a year?
A standard year has 52 weeks and 1 day (365 days divided by 7 = 52.142...). A leap year has 52 weeks and 2 days (366 days). On average, a year has approximately 52.18 weeks. This is why the same date falls on a different day of the week each year.
How many weeks are in a month?
Approximately 4.33 weeks per month on average (52.18 weeks divided by 12 months). Individual months range from about 4 weeks (28-day February in non-leap years) to about 4.43 weeks (31-day months). Because months are not evenly divisible by 7, the number of complete weeks in any given month is either 4 or 5.
How do I count working weeks?
To count working weeks, you need to divide working days by 5 rather than total days by 7. Working days exclude weekends and public holidays. Use a working days calculator to find the number of working days between your dates, then divide by 5 to get working weeks.
Official sources
- MDN Web Docs, JavaScript Date object: developer.mozilla.org.
Reviewed by the CalculatorHub team, edited by James Graham, 14 June 2026. See our methodology.