When to use this calculator
Express a signed calendar-day interval as decimal weeks. Fractional weeks are retained. This is not a count of ISO week labels touched by the interval.
Explore the calendar dates & age calculators for other questions in this topic. For a related calculation, use the Year Progress Calculator: Find the percentage of calendar dates elapsed at the start of a chosen date.
PUTTING IT INTO PRACTICE
Weeks Between Dates: a worked example
The values below are an illustrative example, not a recommendation. Replace them with measurements or assumptions that match your question.
| Input | Example value |
|---|---|
| Start date | 2026-01-01 |
| End date | 2026-01-29 |
| Result | 4 weeks |
- Check the input labels and enter the example values above.
- Apply the relationship: Weeks = calendar-day difference/7..
- The result is 4 weeks, rounded for display.
How to interpret your result
Fractional weeks are retained. This is not a count of ISO week labels touched by the interval.
Choose whether an interval includes the start or end boundary. Month and year additions use explicitly stated clamping rules when a destination day does not exist. Date-only arithmetic is kept independent of local daylight-saving hour shifts.
Frequently asked questions
Does adding one month always add the same number of days?
No. Calendar months vary in length. A day-count addition and a calendar-month addition solve different questions.
When is the weeks between dates calculator useful?
Express a signed calendar-day interval as decimal weeks. Fractional weeks are retained. This is not a count of ISO week labels touched by the interval.
How do I use the weeks between dates calculator?
Enter start date, end date. The result updates automatically. Use the units shown beside each input; the example values illustrate the method.
Which formula does this calculator use?
Weeks = calendar-day difference/7..
What should I check before using the result?
Fractional weeks are retained. This is not a count of ISO week labels touched by the interval.
How are results rounded?
Scalar numbers display up to six decimal places, with scientific notation for very large or small values. Text, fraction, date and schedule outputs use the format described on the tool. Intermediate calculations use JavaScript floating-point arithmetic. Keep sensible precision for your measurements.
Further reading
For background on this topic, see MDN: date values and calendar handling ↗. This is a topic reference, not an external review or endorsement of this tool.
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