How is the number of weeks calculated?

The calculator subtracts the earlier date from the later date in milliseconds, divides by 86,400,000 to get total days, then applies integer division by 7 for full weeks and modulo 7 for the remainder. No network calls are made — everything runs in your browser.

Does the calculator include or exclude the start and end dates?

It measures the gap between the two dates, which is the standard "elapsed time" interpretation. Day 0 is the start date, so a span from Monday to the following Monday is exactly 7 days (1 full week). If you need to count both endpoints add 1 day to either field.

What does "exact weeks (decimal)" mean?

It is the total number of days divided by 7, expressed as a four-decimal fraction. For example, 10 days = 1.4286 weeks. This is useful in project management formulas, Gantt-chart inputs and payroll calculations that accept fractional weeks.

How many weeks are in a year?

A standard Gregorian year has exactly 52 full weeks plus 1 day (365 days total), or 52 weeks plus 2 days in a leap year (366 days). Enter 1 January and 31 December of the same year to confirm this for any specific year.

How many weeks is a pregnancy?

A full-term pregnancy is counted as 40 weeks from the first day of the last menstrual period (LMP). Enter the LMP as the start date and the estimated due date as the end date to verify the interval, or set the start date to today to see how many weeks have elapsed so far.

Can I calculate weeks between dates in different years?

Yes. The calculator handles any span across multiple years, including leap years. The leap-year correction is automatic because the calculation uses real calendar dates rather than a fixed 365-day year.

Weeks Between Dates Calculator

A weeks between dates calculator is one of those deceptively simple tools that comes up in a surprisingly wide range of situations: project planning, pregnancy tracking, academic scheduling, payroll periods, training programmes, lease agreements, and any contract denominated in weeks rather than months. This calculator gives you the answer in under a second — full weeks, leftover days, the decimal equivalent, total days, total hours, and an optional week-by-week breakdown table — all without leaving your browser.

How it works

The core calculation has three steps.

Step 1 — total days. JavaScript represents dates internally as the number of milliseconds since 1 January 1970 (Unix time). Subtracting two Date objects and dividing by 86,400,000 (the number of milliseconds in a day) gives the exact number of elapsed days. The calculation always uses midnight (00:00:00) on each date so the result is a whole number of days.

Step 2 — full weeks and remainder. Integer division by 7 gives the number of complete seven-day weeks. The modulo operation (totalDays mod 7) gives the remaining days that do not make up a full week.

Step 3 — decimal weeks. Dividing total days by 7 without rounding gives the fractional representation, shown to four decimal places. This is useful whenever a formula or spreadsheet expects a continuous numeric value rather than a split whole-number / remainder pair.

The month approximation uses the mean Gregorian month length of 30.4375 days (365.25 / 12), which correctly accounts for the average effect of leap years.

Worked example

Suppose you want to know how many weeks there are between 15 March 2026 and 1 September 2026:

Total days: 170
Full weeks: 24 (24 × 7 = 168)
Remainder days: 2
Exact weeks: 24.2857
Total hours: 4,080
Approx. months: 5.58

If you are planning a 6-month project and your client asks “how many full weekly sprints does that give us?”, the answer is 24 sprints with 2 days of buffer — a directly actionable figure.

Why weeks matter

Many planning frameworks — Agile sprints, academic terms, training blocks, obstetric dating — work natively in weeks rather than months. Months are ambiguous (28, 29, 30 or 31 days), but a week is always exactly 7 days. Using weeks avoids the off-by-one errors that arise when mixing month-length assumptions. The week-by-week breakdown table makes it easy to verify that your sprint schedule or training plan aligns with actual calendar dates, catching cases where a week crosses a bank holiday or a month boundary.

Formula reference

totalDays   = round( |endDate - startDate| / 86_400_000 )
fullWeeks   = floor( totalDays / 7 )
remainder   = totalDays mod 7
exactWeeks  = totalDays / 7
totalHours  = totalDays * 24
approxMonths = totalDays / 30.4375

All arithmetic is integer-exact for days and weeks. The month figure is an approximation because calendar months vary in length.