BCBetter Calculators

Weeks Between Dates Calculator

Calculate the number of weeks between two dates.

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Enter your values and click Calculate

How It Works

The calculator converts both dates to JavaScript Date objects and subtracts them to get total milliseconds, which is divided by 86,400,000 (milliseconds per day) and rounded to get total days. Weeks are found by dividing total days by 7. The whole number of weeks is the floor of that result; the remainder (total days modulo 7) gives the leftover days beyond the last complete week. For example, 85 total days ÷ 7 = 12 whole weeks with 1 remaining day. Approximate months divide total days by 30.4375, the average calendar month length (365.25 ÷ 12), which accounts for leap years over time. Because this calculator uses raw day counts rather than calendar month arithmetic, it avoids the ambiguity caused by months of unequal length and produces consistent, reproducible results regardless of which months fall within the span.

Examples

12-week training plan: Jan 1 to Mar 25
Confirming the duration of a fitness or study program.
Result: 12 weeks and 3 days, 85 total days.
Pregnancy: 40 weeks from Jan 1
Counting gestational weeks from a known start date to an estimated due date.
Result: 40 weeks exactly, 280 days.
6-month subscription: March 1 to September 1
Checking how many weeks are in a 6-month subscription or lease.
Result: 26 weeks and 1 day, 184 total days.

Frequently Asked Questions

How many weeks are in a year?
A standard calendar year has exactly 52 weeks and 1 day (365 days ÷ 7 = 52.143 weeks). A leap year has 52 weeks and 2 days. This is why the day of the week shifts by one each year (or two after a leap year).
How do I count weeks of pregnancy?
Pregnancy is typically measured from the first day of your last menstrual period (LMP), not from conception. Enter your LMP as the start date and today's date or your estimated due date as the end date. A full-term pregnancy is 40 weeks from LMP.
What is the difference between 4 weeks and 1 month?
4 weeks is exactly 28 days. One calendar month averages 30.4375 days, so it is slightly longer than 4 weeks. This means 12 months is not the same as 48 weeks — there are approximately 52.18 weeks in a year. For precise durations, counting in weeks is more accurate than counting in months.

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