How Many Weeks Between Two Dates
Counting weeks between two dates is essential for project planning, academic scheduling, medical tracking, and everyday time management. The core formula is simple—divide the number of days by 7—but deciding between full weeks and partial weeks, understanding ISO week numbering, and knowing how different industries use week counts all add nuance. This guide covers everything you need, including pregnancy week tracking, academic term references, and detailed examples. For instant results, use our weeks & months between dates calculator, or start with the main date calculator to get the day count first.
- Formula: Weeks between = Days between ÷ 7. The quotient is full weeks; the remainder is extra days.
- Full vs. partial weeks: 50 days = 7 full weeks + 1 day, or approximately 7.14 weeks.
- ISO week numbering (ISO 8601) defines weeks as starting on Monday, with week 1 being the first week containing a Thursday.
- Pregnancy: Full-term = 40 weeks (280 days), divided into 3 trimesters.
- Common durations: Academic semester = ~15 weeks, fiscal quarter = 13 weeks, year = 52 weeks + 1 day.
- See our days to weeks conversion guide for detailed conversion tables.
How to Calculate Weeks Between Two Dates
The calculation is a two-step process:
- Count the total days between your two dates. (See our days between dates guide for the detailed method.)
- Divide by 7 to convert days to weeks.
Weeks = Days ÷ 7
Worked Example
How many weeks between January 6, 2025 and April 14, 2025?
- Days in January remaining after Jan 6: 31 − 6 = 25
- February: 28 days (2025 is not a leap year)
- March: 31 days
- April 1–14: 14 days
- Total: 25 + 28 + 31 + 14 = 98 days
- 98 ÷ 7 = 14 weeks exactly
This date range is exactly 14 weeks—a common sprint-planning boundary. Our date calculator confirms this instantly.
Full Weeks vs. Partial Weeks
When the day count is not evenly divisible by 7, you have to decide how to handle the remainder:
| Method | Description | Example (50 days) |
|---|---|---|
| Full weeks only | Drop the remainder; count only complete 7-day cycles | 7 weeks |
| Weeks + remaining days | Report full weeks plus leftover days | 7 weeks, 1 day |
| Decimal weeks | Divide days by 7 and express as a decimal | 7.14 weeks |
| Round up (ceiling) | Round up to the next whole week | 8 weeks |
The best method depends on context. Project managers often round up (to ensure enough sprint cycles). Medical professionals use weeks + days (e.g., “32 weeks and 4 days pregnant”). Financial analysts may prefer decimal weeks for precision.
Week Calculation Examples
The following table shows how common day counts convert to weeks. Use these as a quick reference, or try our weeks between dates calculator for any custom range.
| Days | Full Weeks | Weeks + Days | Decimal Weeks |
|---|---|---|---|
| 7 | 1 | 1 week, 0 days | 1.00 |
| 14 | 2 | 2 weeks, 0 days | 2.00 |
| 30 | 4 | 4 weeks, 2 days | 4.29 |
| 45 | 6 | 6 weeks, 3 days | 6.43 |
| 60 | 8 | 8 weeks, 4 days | 8.57 |
| 90 | 12 | 12 weeks, 6 days | 12.86 |
| 120 | 17 | 17 weeks, 1 day | 17.14 |
| 180 | 25 | 25 weeks, 5 days | 25.71 |
| 365 | 52 | 52 weeks, 1 day | 52.14 |
Pregnancy Weeks Reference
Pregnancy is one of the most common contexts where weeks are the primary unit of measurement. The American College of Obstetricians and Gynecologists (ACOG) defines a full-term pregnancy as 40 weeks (280 days) from the first day of the last menstrual period (LMP).
Trimester Breakdown
| Trimester | Weeks | Days | Key Milestones |
|---|---|---|---|
| First Trimester | 1–12 | 1–84 | Conception, heartbeat detected (~6 weeks), first ultrasound (~8–12 weeks) |
| Second Trimester | 13–27 | 85–189 | Anatomy scan (~20 weeks), fetal movement felt (~16–25 weeks) |
| Third Trimester | 28–40 | 190–280 | Viability milestone (~24 weeks), full term (~39–40 weeks) |
Important Pregnancy Week Markers
- Week 8: First prenatal visit and initial bloodwork
- Week 12: End of first trimester; risk of miscarriage drops significantly
- Week 20: Anatomy scan (mid-pregnancy ultrasound); halfway point
- Week 28: Third trimester begins; glucose screening test
- Week 37: Baby is considered “early term”
- Week 39–40: Full term; most deliveries occur in this window
- Week 42: Post-term; induction is typically recommended
Medical professionals express gestational age as “weeks + days” (e.g., “32 weeks and 4 days” or “32+4”). Use our weeks between dates calculator to track pregnancy progress from LMP to any given date, or the add days calculator to find your estimated due date (LMP + 280 days).
Academic Term Weeks Reference
Educational institutions worldwide structure their calendars around week counts. Knowing the exact number of weeks in a term helps with syllabus planning, assignment scheduling, and exam preparation.
| System | Weeks | Approximate Days | Typical Use |
|---|---|---|---|
| US Semester | 15–16 | 105–112 | Most US universities; fall and spring terms |
| US Quarter | 10–11 | 70–77 | Some US universities (e.g., UC system, Stanford) |
| UK Trimester | 10–12 | 70–84 | British universities; three terms per year |
| Summer Session | 6–8 | 42–56 | Accelerated courses; compressed scheduling |
| Mini-mester | 3–4 | 21–28 | January or May intensive terms |
| K-12 School Year | 36–40 | 180 instruction days | US public schools (typically ~180 school days) |
A common planning approach is to count weeks between the first and last day of the term using our calculator, then allocate content across those weeks. For US colleges, the National Center for Education Statistics provides data on academic calendars by institution.
Common Time Periods Expressed in Weeks
Many important durations are naturally measured in weeks. Here is a reference table.
| Duration | Weeks | Days | Context |
|---|---|---|---|
| 1 month (average) | ~4.35 | 30.44 | Calendar approximation |
| 6 weeks | 6 | 42 | Post-surgical recovery check |
| Academic quarter | 10–11 | 70–77 | US university quarter system |
| Fiscal quarter | 13 | 91 | Business/financial reporting |
| Academic semester | 15–16 | 105–112 | US university semester system |
| Half year | ~26 | 182–183 | Semi-annual reviews |
| Pregnancy (full term) | 40 | 280 | Obstetric standard |
| One year | 52 + 1 day | 365 | Standard calendar year |
A fiscal quarter of 13 weeks is used in many corporate environments because 4 × 13 = 52 weeks, which neatly divides a year into four equal parts. Some companies use a 4-4-5 week calendar (4 weeks + 4 weeks + 5 weeks per quarter) for even more precise financial reporting.
ISO Week Numbering (ISO 8601)
The ISO 8601 standard defines an international week-numbering system used in business, IT, and government across Europe and much of the world.
Key Rules
- Weeks start on Monday (not Sunday, as is common in the US).
- Week 1 of a year is the first week that contains a Thursday—equivalently, the week containing January 4.
- A year has either 52 or 53 ISO weeks.
- Dates in the ISO week system are written as YYYY-Www-D (e.g., 2025-W14-1 for Monday of week 14 in 2025).
Why ISO Weeks Matter
If you are counting weeks between dates for international business, logistics, or software systems, ISO week numbers ensure everyone agrees on which week is which. A date in “Week 1” under the US convention might fall in “Week 53” of the previous year under ISO 8601, leading to confusion if systems are not aligned.
Learn more about the ISO week date format on Wikipedia.
Industry Use Cases for Week Counting
Sprint Planning (Agile/Scrum)
Agile development teams work in sprints, typically 1, 2, or 4 weeks long. If a product launch is 90 days away, converting to weeks (12 weeks + 6 days) tells the team they have roughly 6 two-week sprints to deliver. Our weeks between dates calculator makes this conversion effortless.
Medical Follow-Ups
Doctors schedule follow-up appointments in weeks: “Come back in 6 weeks” (42 days), “recheck in 12 weeks” (84 days). Pregnancy is tracked entirely in weeks, with specific tests and milestones at weeks 8, 12, 20, 28, 36, and 40. The ACOG guidelines are built around these week markers.
Fitness and Training Programs
Running plans (5K, 10K, half marathon, marathon) are structured by week. A typical Couch-to-5K program runs 9 weeks; a marathon training plan runs 16–20 weeks. Athletes count weeks between their current date and race day to ensure they are on schedule.
Employee Onboarding
Many organizations structure onboarding over a set number of weeks: week 1 for orientation, weeks 2–4 for training, weeks 5–8 for shadowing, and a performance review at week 12. Counting weeks between the hire date and milestones keeps HR on track.
Frequently Asked Questions
First, count the total number of days between the two dates. Then divide by 7. The whole-number result is the number of full weeks; the remainder is the extra days. For example, 100 days ÷ 7 = 14 weeks and 2 days. Use our weeks between dates calculator for instant results.
No. The only month that is exactly 4 weeks is February in a non-leap year (28 days). All other months are longer: 30 or 31 days, which equals 4 weeks plus 2 or 3 extra days. On average, a month is about 4.35 weeks (30.44 days ÷ 7). This is why “4 weeks” and “1 month” are not interchangeable.
A standard year has 365 days, which equals 52 weeks and 1 day. A leap year has 366 days, which equals 52 weeks and 2 days. Under the ISO 8601 system, most years have 52 numbered weeks, but some “long years” have 53. See our days in a year guide for more detail.
Pregnancy weeks are counted from the first day of the last menstrual period (LMP), not from conception. A full-term pregnancy is 40 weeks (280 days). Trimesters are: first (weeks 1–12), second (weeks 13–27), and third (weeks 28–40). The standard is set by the ACOG, and preterm birth is defined as delivery before 37 weeks.
ISO week numbering is defined by the ISO 8601 standard. Weeks start on Monday, and week 1 is the first week of the year containing a Thursday (or equivalently, the week containing January 4). Most years have 52 ISO weeks; some have 53. This system is widely used in European business, logistics, and IT systems.
A typical US college semester is 15 to 16 weeks of instruction, plus 1–2 weeks for finals. The exact number varies by institution. A quarter is shorter at 10–11 weeks. Summer sessions are typically 6–8 weeks. Use our calculator to count the exact weeks between your term start and end dates.
A full-term pregnancy is 40 weeks (280 days) from the first day of the last menstrual period. This is the standard used by the ACOG. Preterm birth is defined as delivery before 37 weeks. Post-term is after 42 weeks, at which point induction is typically recommended.