Date Difference in Weeks

Enter two dates; the tool returns the exact number of weeks between them, including a fractional remainder for partial weeks. Negative values appear when the second date is earlier than the first.

Use it for project planning that runs in weekly sprints, pregnancy or medical timelines, or any context where weeks are the natural unit. The math is straightforward — days divided by 7 — but the tool also breaks out full weeks plus leftover days, which is more readable than 12.857 weeks.

Dates are interpreted in your local timezone. For UTC-based calculations (server logs, multi-zone analyses), pick the explicit UTC option from the timezone dropdown.

The core calculation: difference in milliseconds between the two dates, divided by 604,800,000 (the number of milliseconds in a 7-day week). The result is a fractional number of weeks; the tool also breaks it out into integer weeks plus residual days for readability. Both dates are interpreted in the selected timezone (defaulting to local) so daylight-saving transitions don't introduce off-by-one-day errors at the edges of the calculation.

Worked example. Start: 2026-01-01. End: 2026-04-15. Difference: 104 days = 14.857 weeks = 14 weeks plus 6 days. Reverse the dates and you get -14.857 weeks. The fractional portion shows when the answer doesn't cleanly divide — for sprint planning over 105 days (15 weeks exactly), the fraction is .000; for 104 days, .857; for 110 days, .714 (110/7).

Gotchas around timezones. If the two dates are in different timezones (a meeting between New York and Tokyo, for instance), the week count depends on which timezone you anchor to. The tool's default is local-machine timezone for both dates, with an explicit override per field. For UTC-anchored calculations (server logs, financial settlement dates, scientific timestamps), pick UTC explicitly — the local-time defaults can introduce DST-shifted hours that don't actually exist in some calculations.

Use cases. Pregnancy timelines are conventionally measured in weeks plus days from the last menstrual period. Project planning runs in weekly sprints ("sprint 4 of 12 means 12 weeks committed"). Subscription billing on weekly cycles. Animal gestation periods. Each of these contexts uses week-based math, and getting the residual day count right matters for scheduling.

A contrarian opinion: weeks aren't always the natural unit. For periods longer than 13 weeks (a quarter), most people switch to months, even though month-counts are messier (variable days per month, depending on which months are in the range). For periods shorter than 4 weeks, day counts are usually clearer. The tool computes weeks because that's what was asked, but consider whether the audience actually thinks in weeks for the duration in question.