Weeks between two dates
Count the complete weeks and leftover days separating two dates.
Calculator inputs
Results
Enter your values and press “Calculate” to see the result.
In short
- What it calculates
- Count the complete weeks and leftover days separating two dates.
- Formula used
Complete weeks = days ÷ 7 (whole part)- Example
- From 2026-01-01 to 2026-03-15
Weeks between two dates
Many timelines are expressed in weeks: pregnancies, project deliveries, training plans or courses.
Here you get both the complete weeks and the days left over.
How it works
Calendar days between the two dates are counted and divided by seven. The whole part gives the complete weeks and the remainder gives the leftover days.
Formula
Complete weeks = days ÷ 7 (whole part)
Leftover days = days modulo 7
Decimal weeks = days ÷ 7
Worked example
From 2026-01-01 to 2026-03-15
Days: 73
73 ÷ 7 = 10 weeks and 3 days
As a decimal: 10.43 weeks
Explanation
Complete weeks and started weeks
Between two dates seventeen days apart there are two complete weeks and three days, or almost two and a half weeks depending on how you express it. In contractual and project deadlines it pays to clarify whether complete or started weeks are counted, because the difference can be a full seven days.
The ISO week starts on Monday
The international standard sets Monday as the first day and defines week one of the year as the one containing the first Thursday. That is why 1 January can fall in week 52 or 53 of the previous year, which surprises people planning production calendars.
Pregnancy weeks
In obstetrics they are counted from the first day of the last menstrual period, and expressed as weeks plus days: 12+3 means twelve weeks and three days. It is a very specific usage that does not match the civil calculation of weeks between two dates.
Sprint planning
Teams working in two or three week cycles use this calculation to know how many iterations fit between today and a delivery date, and to distribute scope accordingly.
Frequently asked questions
How do I count pregnancy weeks?
Use the date of the last period as the start. For more detail, the gestational age calculator does it directly.
Is the final day counted?
No. The plain difference between the two dates is calculated.
Why can 1 January fall in week 53?
Because the ISO standard defines week one as the one containing the year's first Thursday. If 1 January falls on a Friday, Saturday or Sunday, it belongs to the last week of the previous year.
Does it work for counting pregnancy weeks?
The civil calculation differs from the obstetric one, which starts from the first day of the last period and is expressed as weeks plus days.
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