Weeks Between Dates Calculator
How Many Weeks Between Two Dates
Add or Subtract Weeks from a Date
Date Information
How it works
Put the earlier date in Start and the later one in End, and the answer appears as you type. You get it three ways, because “how many weeks” means three different things depending on who is asking.
Weeks and days is the human answer: 6 weeks 3 days. This is what you want for a pregnancy dating, a training block, a notice period, or anything you would say out loud.
Total weeks is the same span as a single decimal number: 6.43. This is the answer a spreadsheet wants, and it is the day count divided by 7. It is deliberately not rounded to a whole week, because rounding hides up to three days of error, and those days matter when you are checking whether something fits inside a deadline.
Total days is the raw span, and it is the number everything else is derived from. The count is exclusive of the start date and inclusive of the end date: 1 January to 31 January is 30 days, not 31. That is the convention used by notice periods, interest periods and hotel nights. If you want the inclusive count (the number of calendar squares the range touches, which is what you want for holiday entitlement or days of attendance), add one.
Weeks since a date. Leave End on today and put the past date in Start. Both fields default to today, so you only have to change one. Weeks until a date works the same way with the roles reversed: today in Start, the future date in End. A negative result means the two are the wrong way round, and the magnitude is still correct.
Adding and subtracting weeks. The second panel moves a date forwards or backwards, and it defaults to weeks, so “3 weeks from 18 May” is one field and one number. Adding weeks is exact, because a week is always 7 days with no month-length or leap-year complications, so the result always lands on the same weekday as the start date. That property is what makes weeks the unit of choice for sprints, payroll cycles, chemotherapy schedules and course timetables.
A fortnight is two weeks, so halve the total-weeks figure. A calendar month is not four weeks: it averages 4.35, which is why “four weeks” and “a month” drift apart by roughly two days a month and by about four and a half weeks over a year.
ISO week numbers are in the third panel, and they answer a different question from the count above. An ISO week number identifies which week of the year a date falls in (1 to 52 or 53, Monday to Sunday), rather than how many weeks separate two dates. European manufacturing, logistics and project planning run on them: “delivery in week 34”.
All arithmetic runs in UTC at midnight. Doing date maths in local time is the classic source of off-by-one-day results, because a day is 23 or 25 hours long when the clocks change. Pinning everything to UTC gives the same answer in March as in July, and the same answer in Auckland as in Los Angeles.
For a live countdown to one date, the Days Until Calculator on this site gives the days, weeks and working days left until Christmas, Easter or any date you pick.
Everything is computed by JavaScript in your browser. There is no backend and no request is made when you change a date. Open DevTools, go to the Network tab, and use the tool to confirm.
Frequently Asked Questions
How many weeks are between two dates?
- Count the days between them and divide by 7. This tool does both at once and shows the result two ways: as whole weeks plus leftover days (the human answer, e.g. 6 weeks 3 days) and as a single decimal (6.43). The day count is exclusive of the start date and inclusive of the end date, matching how notice periods and interest periods are counted.
How many weeks since a given date?
- Leave the End field on today (it already defaults to today) and set Start to the past date. The Weeks and days row is your answer. For weeks until a future date, put today in Start and the future date in End. Filling them the other way round gives a negative number of the same size, which is still the right answer.
Does the count include the start date?
- No. The span is exclusive of the start date and inclusive of the end date, so 1 January to 31 January is 30 days and 4 weeks 2 days. That is the convention used for contracts, interest and hotel nights. If you need the inclusive count, every calendar day the range touches, add 1 to the total days before dividing by 7.
Why is Total weeks a decimal instead of a whole number?
- Because rounding would hide up to three days. 45 days is 6.43 weeks; rounded to “6 weeks” you lose three days, and rounded to 6½ you gain half a day. When you are checking whether a task fits inside a deadline, those days are the whole point. The Weeks and days row gives you the exact remainder if you prefer it in that form.
Is a month four weeks?
- No, and this is the most common source of scheduling errors. Four weeks is 28 days; the average calendar month is 30.44 days, or 4.35 weeks. Over a year the gap compounds: 13 four-week cycles fit into 364 days, so a “monthly” thing scheduled every four weeks happens 13 times a year rather than 12. Use the calendar-month figure on the Date Calculator when you mean months.
How many weeks are in a year?
- 52 weeks and 1 day in a common year, 52 weeks and 2 days in a leap year. That leftover day is why your birthday shifts forward one weekday each year, and two after a leap day. In ISO week numbering most years have 52 weeks and roughly one year in six has 53.
How do I add or subtract weeks from a date?
- Use the second panel. It defaults to weeks, so you set the base date, type the number, and pick Add or Subtract. Week arithmetic is exact, since a week is always 7 days, so the result always falls on the same weekday as the date you started from. That is not true of months or years, which have to clamp to the end of a short month.
What date is 2 weeks after a date?
- Two weeks is exactly 14 days, and week arithmetic always lands on the same weekday: 2 weeks after Monday 5 May 2025 is Monday 19 May 2025. Use the second panel: set the base date, type 2, leave the unit on weeks and pick Add. Subtract runs it backwards, so 2 weeks before 5 May 2025 is Monday 21 April 2025.
How many weeks from September to January?
- From 1 September to 1 January is 122 days, which is 17 weeks 3 days, or 17.43 weeks. Carry on to 31 January and it is 152 days, which is 21 weeks 5 days, or 21.71 weeks. Both counts are exclusive of the start date and inclusive of the end date; put your own two dates in the fields for the exact figure.
What is a fortnight, and how many fortnights are between two dates?
- A fortnight is exactly two weeks, or 14 days, and it is the standard pay period in the UK, Ireland, Australia and New Zealand. Halve the Total weeks figure to get fortnights: 12.86 weeks is 6.43 fortnights. To step forwards by fortnights, put an even number of weeks in the Add panel.
What is an ISO week number, and is it the same as the weeks between two dates?
- No, they answer different questions. The weeks between two dates measures a span. An ISO week number identifies which week of the year a single date falls in (1 to 52 or 53, running Monday to Sunday), with week 1 being the week that contains the first Thursday of January. The third panel gives the ISO week number for any date. A consequence of the rule: 1–3 January can belong to the last week of the previous year, and 29–31 December can belong to week 1 of the next.
Does it count working weeks or exclude holidays?
- It counts calendar weeks, weekends included. The Date Calculator on this site has a working-days figure that excludes Saturdays and Sundays; divide that by 5 for working weeks. Neither tool knows about public holidays, because they vary by country, by region and sometimes by employer, and a wrong holiday list is worse than none.
Does daylight saving time affect the result?
- No. All arithmetic is done in UTC at midnight, so the 23-hour and 25-hour days that occur when the clocks change never enter the calculation. Date maths done in local time is the usual cause of results that are one day out, and this tool sidesteps it entirely.
Is my data safe?
- Yes. This is a static client-side page with no backend. Your dates are processed by JavaScript inside your browser tab and are never transmitted anywhere. You can confirm by opening DevTools and watching the Network tab: using the tool produces zero outbound HTTP requests.
Common spans in weeks
Quick conversions between days, weeks and the units people actually schedule in.
| Span | Days | Weeks | Notes |
|---|---|---|---|
| 1 fortnight | 14 | 2 | Standard pay period in the UK, Ireland, Australia and NZ |
| 1 calendar month (average) | 30.44 | 4.35 | Not 4: the gap is about 2.4 days per month |
| 1 quarter | 91.31 | 13.04 | 13 weeks is the usual planning approximation |
| 1 common year | 365 | 52.14 | 52 weeks and 1 day |
| 1 leap year | 366 | 52.29 | 52 weeks and 2 days |
| Full-term pregnancy | 280 | 40 | Counted from the last menstrual period, not conception |
| Standard sprint | 14 | 2 | Two weeks is the most common Scrum cadence |
| School year (UK/US) | ~273 | ~39 | About 39 teaching weeks across three terms |
The average calendar month is 365.2425 ÷ 12 = 30.44 days under the Gregorian rule. Anything scheduled “every four weeks” recurs 13 times a year, not 12.