Weeks and Months Between Dates
Calculate the number of weeks and months between any two dates. Useful for pregnancy tracking, project timelines, lease durations, and academic planning. Our calculator shows total days, weeks, months, years, weekdays, weekend days, hours, and a natural language summary.
- 1 week = 7 days (exact)
- 1 month = ~30.44 days (average)
- 1 year = 52.14 weeks or 12 months or 365.25 days (average)
- Pregnancy = 40 weeks from last menstrual period (not 9 calendar months)
- Related: Weeks guide · Months guide · Days to weeks
Calculate Weeks & Months
Enter two dates to find the duration in weeks, months, and more
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How Weeks and Months Are Calculated
Calculating weeks between two dates is straightforward: divide the total number of days by 7. Since a week is always exactly 7 days, this gives a precise result. For example, 21 days is always exactly 3 weeks, and 100 days is exactly 14 weeks and 2 days.
Months, however, are more complicated because calendar months vary in length from 28 to 31 days. February has 28 days (29 in a leap year), while January, March, May, July, August, October, and December each have 31 days. The remaining months have 30 days. This variability means that "one month from today" can represent different numbers of days depending on which month you start in.
To handle this inconsistency, date calculators typically use the average month length of 30.44 days (365.25 days per year divided by 12 months). The 365.25 figure accounts for leap years, which occur every 4 years. The ISO 8601 standard defines week numbering for international consistency, where weeks start on Monday and Week 1 contains the first Thursday of the year.
When precision matters -- for example in legal contracts or medical contexts -- it is important to distinguish between calendar months (the actual span from one date to the same date next month) and average months (total days divided by 30.44). Our calculator uses the average method for its decimal month value, while the breakdown text shows exact weeks and remaining days for clarity.
Pregnancy & Trimester Tracker
One of the most common reasons people calculate weeks between dates is for pregnancy tracking. A standard pregnancy lasts approximately 40 weeks (280 days) from the first day of the last menstrual period (LMP), not the commonly quoted "9 months." In reality, 40 weeks equals about 9 months and 1 week. The American College of Obstetricians and Gynecologists (ACOG) defines pregnancy trimesters as follows:
| Trimester | Weeks | Months | Key Milestones |
|---|---|---|---|
| 1st Trimester | 1-12 | 1-3 | Heartbeat detected (6 wk), major organs form, first ultrasound |
| 2nd Trimester | 13-26 | 4-6 | Gender visible (18-20 wk), fetal movement felt, anatomy scan |
| 3rd Trimester | 27-40 | 7-9+ | Lungs mature (34 wk), head engages, full term at 39 weeks |
Important note: Pregnancy is dated from the last menstrual period, meaning conception typically occurs around week 2. A baby born at 37-38 weeks is considered "early term," while 39-40 weeks is "full term." Use our weeks between dates guide to track your pregnancy progress week by week.
Common Duration Reference
This quick-reference table converts common time periods between days, weeks, and months:
| Period | Days | Weeks | Months | Common Context |
|---|---|---|---|---|
| 1 week | 7 | 1 | 0.23 | Sprint cycle, weekly review |
| 2 weeks | 14 | 2 | 0.46 | Agile sprint, pay period |
| 1 month | 30-31 | 4.3 | 1 | Billing cycle, rent period |
| 6 weeks | 42 | 6 | 1.38 | Postpartum recovery, short course |
| 2 months | 61 | 8.7 | 2 | Visa processing, notice period |
| Quarter | 91 | 13 | 3 | Fiscal quarter, academic term |
| Half year | 183 | 26.1 | 6 | Semester, semi-annual review |
| 9 months | 274 | 39.1 | 9 | Pregnancy (approx.), school year |
| 1 year | 365 | 52.1 | 12 | Annual lease, subscription |
| 18 months | 548 | 78.3 | 18 | Toddler milestone, MBA program |
| 2 years | 730 | 104.3 | 24 | Phone contract, warranty period |
Conversion Tables
Days to Weeks
| Days | Weeks | Weeks + Days |
|---|---|---|
| 7 | 1 | 1 week |
| 14 | 2 | 2 weeks |
| 21 | 3 | 3 weeks |
| 28 | 4 | 4 weeks |
| 30 | 4.3 | 4 weeks, 2 days |
| 60 | 8.6 | 8 weeks, 4 days |
| 90 | 12.9 | 12 weeks, 6 days |
| 180 | 25.7 | 25 weeks, 5 days |
| 365 | 52.1 | 52 weeks, 1 day |
Weeks to Months
| Weeks | Months | Common Use |
|---|---|---|
| 4 | 0.92 | ~1 month |
| 8 | 1.84 | ~2 months |
| 12 | 2.76 | ~3 months (1st trimester) |
| 16 | 3.68 | ~4 months |
| 20 | 4.60 | ~5 months |
| 24 | 5.52 | ~6 months (2nd trimester) |
| 40 | 9.21 | ~9 months (pregnancy) |
| 52 | 11.96 | ~12 months (1 year) |
Weeks in Each Month (2026)
Every month contains at least 4 full weeks, but the extra days vary. Here is the breakdown for 2026:
| Month | Days | Full Weeks | Extra Days |
|---|---|---|---|
| January | 31 | 4 | 3 |
| February | 28 | 4 | 0 |
| March | 31 | 4 | 3 |
| April | 30 | 4 | 2 |
| May | 31 | 4 | 3 |
| June | 30 | 4 | 2 |
| July | 31 | 4 | 3 |
| August | 31 | 4 | 3 |
| September | 30 | 4 | 2 |
| October | 31 | 4 | 3 |
| November | 30 | 4 | 2 |
| December | 31 | 4 | 3 |
| Total | 365 | 52 | 1 |
Note that 2026 is not a leap year, so February has exactly 4 weeks with no extra days. The total of 365 days equals 52 full weeks plus 1 extra day, which is why the year advances by one day of the week each non-leap year.
Use Cases for Week/Month Calculations
Pregnancy Tracking
Expectant parents frequently need to convert between weeks and months when communicating with healthcare providers and family members. Doctors track pregnancy in weeks (e.g., "you are 24 weeks along"), while family and friends tend to think in months. Our calculator helps bridge this gap. For a detailed breakdown of pregnancy week counting, see our how many weeks between dates guide. Knowing your exact week count helps schedule prenatal appointments, screenings, and prepare for each trimester's milestones.
Project Management & Sprint Planning
Software development teams using Agile methodologies work in sprints, typically lasting 1-2 weeks. Project managers need to calculate how many sprints fit into a project timeline, which requires converting months or quarters into weeks. For instance, a 3-month project spans approximately 13 weeks or 6-7 two-week sprints. Knowing the exact week count also helps with resource allocation, milestone planning, and burndown chart projections across the full project lifecycle.
Rental & Lease Calculations
Landlords and tenants often need to convert between weeks and months for short-term rentals, vacation properties, and pro-rated rent calculations. A "month-to-month" lease covers different numbers of days depending on the calendar month, while weekly rentals are always exactly 7 days. Understanding that a month is not exactly 4 weeks (it is approximately 4.35 weeks) prevents billing disputes and ensures accurate month-based calculations.
Academic Terms & Semesters
Students and educators plan around academic terms measured in weeks. A typical US college semester runs 15-16 weeks, while a quarter system uses 10-11 week terms. Knowing the exact number of weeks remaining in a term helps with study schedules, assignment planning, and exam preparation. International programs may use different term lengths, making a weeks-and-months calculator essential for exchange students comparing academic calendars.
Frequently Asked Questions
To find the weeks between two dates, calculate the total number of days between them and divide by 7. For example, 45 days equals 6 weeks and 3 days. Our weeks and months calculator does this automatically, showing both the decimal value and the exact weeks-plus-days breakdown.
From January 1 to December 1 is exactly 11 calendar months, or 334 days (in a non-leap year). From January 1 to December 31 is 364 days, which equals approximately 11.96 months using the 30.44-day average. Use our months between dates guide for more examples.
No. Four weeks equals exactly 28 days, but most months have 30 or 31 days. Only February in a non-leap year has exactly 4 weeks. On average, a month is approximately 4.35 weeks (30.44 days divided by 7). See our weeks to months conversion guide for a detailed breakdown.
Pregnancy weeks are counted from the first day of your last menstrual period (LMP). Enter your LMP as the start date and today as the end date in our calculator. A full-term pregnancy is 40 weeks. For more details, see our weeks between dates guide or consult ACOG guidelines.
A standard year has 52 weeks and 1 day (365 days). A leap year has 52 weeks and 2 days (366 days). The average year length of 365.25 days works out to approximately 52.18 weeks. The days in a year guide covers this in detail.
The number of weeks until Christmas changes daily. Use our Christmas countdown calculator for a live count, or enter today's date and December 25 into the calculator above. You can also check our weeks until Christmas guide for planning milestones.
A calendar month runs from a date in one month to the same date in the next (e.g., March 15 to April 15). An average month is a fixed 30.44 days, used when dividing total days by a standard month length. Calendar months are used in leases and contracts; average months are used in duration calculations.
Multiply the number of weeks by 7 to get days, then divide by 30.44 to get average months. For example, 12 weeks = 84 days = 2.76 months. Alternatively, divide weeks by 4.345 for a quick estimate. See our weeks to months conversion guide for a complete reference table.