How Many Weeks Between Two Dates? Easy Methods to Calculate

You have a deadline in ten weeks and a project start date that feels distant. Figuring out exactly how many weeks sit between two dates can save you from calendar confusion and missed milestones. This guide walks through manual calculations, Excel formulas, and online tools so you can get a precise week count every time.

Average weeks per year: 52.1775 ·
Days per week: 7 ·
Approx. weeks in a typical year: 52 ·
Weeks between two dates (method): days ÷ 7 ·
Common uses: planning, tracking, delivery dates

Here is a reference table of key calendar values used throughout this guide.

How many weeks between two dates?

This is the core question anyone with a deadline or event date asks. The answer always starts with counting total days and dividing by 7.

Manual calculation: divide days by 7

To manually find the number of weeks between two dates, you first calculate the total number of days between them. A standard method from Inch Calculator (practical math reference) involves subtracting the start day from the total days in the start month, adding the end month’s day, then adding all days from interim months. Finally, divide that total by 7 to get weeks.

1. Identify the start and end dates.
2. Subtract the start day from total days in the start month.
3. Add the day of the end month.
4. Add days from full interim months.
5. Divide total days by 7.

For full weeks only, round the result down. Planetcalc (online calculation utility) recommends dividing days by 7 and rounding down for full weeks while noting the remainder as extra days.

Using a week calculator online

Online week calculators simplify the process. Enter the start and end dates, and the tool returns weeks and remaining days. DQYDJ (financial and time calculator site) shows weeks, days, total days, months, and decimal weeks. Omni Calculator (everyday life tool) excludes the starting day from the count, so check your tool’s default behavior.

The pattern: online tools automatically account for leap years and varying month lengths, making them reliable for cross-year spans.

How do I calculate weeks between dates in Excel?

Excel offers multiple formulas, each suited to different needs — from simple week counts to business-day calculations.

Using the DATEDIF function

Excel’s DATEDIF function with the “d” argument returns the number of days between two dates. Divide that result by 7 for weeks. For whole weeks, wrap it in INT(). According to Trump Excel (Excel tutorial resource), the formula =INT(DAYS(B2,A2)/7) gives completed full weeks. Alternatively, =ROUNDUP(DAYS(B2,A2)/7,0) rounds up to the nearest whole week.

• Simple subtraction: =(B2-A2)/7 — gives a decimal week value.
• DAYS function: =DAYS(end_date, start_date)/7 — clearer syntax.
• WEEKNUM approach (same year only): =WEEKNUM(end_date) - WEEKNUM(start_date) — works within a single calendar year.

The catch WEEKNUM fails across years. As Smartsheet Community (project management forum) notes, if the two dates cross year boundaries, the WEEKNUM difference becomes inaccurate — stick to days divided by 7 for cross-year spans.

Using the NETWORKDAYS function for business weeks

For project management, business weeks matter more than calendar weeks. Excel’s NETWORKDAYS function counts only weekdays (Monday through Friday) between two dates. Divide that count by 5 to get business weeks. Trump Excel (Excel tutorial resource) demonstrates this approach for delivery schedules and work timelines.

The catch: Using calendar days for a business timeline inflates capacity by 40 percent, which leads to missed deadlines.

What is a week calculator by date for pregnancy?

Pregnancy week calculators are one of the most common use cases for date-to-week calculations. They estimate due dates based on the first day of the last menstrual period (LMP).

How pregnancy weeks are calculated from last menstrual period

Pregnancy is typically 40 weeks from the first day of the LMP. According to U.S. Centers for Disease Control and Prevention (CDC) (public health authority), this 40-week standard is the foundation for due date estimates. Week calculators add 280 days to the LMP date, then divide the span into 40 weeks.

Using a due date predictor

Online due date predictors use the same principle: enter your LMP and the tool calculates the estimated due date. However, exact results can vary. Different formulas — Naegele’s rule versus ultrasound-based dating — may produce slightly different dates. The CDC (public health authority) recommends ultrasound confirmation for the most accurate estimate.

The trade-off: Naegele’s rule assumes a 28-day cycle, while real cycles vary. A woman with a 35-day cycle might get a different due date from a calculator than her clinician would estimate.

The pattern: Any pregnancy calculator carries a margin of error equal to the difference between a standard 28-day cycle and the individual’s actual cycle length.

How many weeks from date to date?

This question covers any pair of dates, not just pregnancy or work. The method is universal: count total days, divide by 7, and interpret the result.

Finding the number of weeks between any two dates

The process works identically whether you calculate for a wedding countdown, a subscription renewal, or a school term. Planetcalc (mathematics utility site) provides a straightforward tool that inputs two dates and returns weeks, days, and the remainder. For manual calculation, Inch Calculator (practical math reference) breaks it into four clear steps: subtract start day from start month’s days, add end month’s day, add interim full months’ days, then divide by 7.

Accounting for partial weeks

Not every date range divides evenly into whole weeks. For example, from a Monday to the following Sunday is 6 days: 0 full weeks with 6 remainder days. Express this as 0.86 weeks. DQYDJ (financial and time calculator site) outputs decimal weeks alongside whole weeks and days, giving you both precision and readability.

What this means: A freelancer billing by the week who finishes a project on a Wednesday must decide whether to charge 2.0 weeks or 2.14 weeks.

How many weeks in December?

December has 31 days, which is 4 full weeks and 3 days. Depending on the year’s starting day of the week, December may span parts of 5 calendar weeks.

The number of days in December

December always has 31 days, according to standard calendar conventions used by Inch Calculator (calendar reference). This makes it one of seven months with 31 days.

Why it varies from 4 to 5 weeks depending on the year’s start

A week that starts on December 1 might end in the next calendar year, or a week ending on December 31 might have started in November. For planning purposes, knowing whether December spans 4 or 5 calendar weeks matters for payroll periods, school terms, and billing cycles.

The pattern: Your “weeks in December” depends on how you define the week boundary — Sunday vs. Monday starts, and whether weeks must be wholly contained in the month. Smartsheet Community (project management forum) discussion highlights that this ambiguity affects project timeline reporting.

The catch: A payroll manager counting December as 4 weeks will underpay employees if the month actually spans 5 partial weeks.

Using Google Sheets for weeks between dates

Google Sheets mirrors Excel’s formulas with the same DAYS and DATEDIF functions. A YouTube tutorial (spreadsheet instructional channel) demonstrates that =INT(DAYS(end,start)/7) yields full weeks without decimals. For whole weeks rounded down, the Google Docs Support (official platform help) recommends =ROUNDDOWN(DATEDIF(start,end,"D")/7,0).

Pregnancy is typically 40 weeks from the first day of the last menstrual period.

U.S. Centers for Disease Control and Prevention (CDC) (public health authority)

The DATEDIF function calculates the number of days, months, or years between two dates — dividing by 7 yields weeks.

Microsoft Office Support via Trump Excel (Excel documentation resource)

Whether you count manually, in a spreadsheet, or with an online tool, the math stays the same: total days divided by 7. For anyone managing a project timeline, tracking a pregnancy, or planning a vacation, that simple division determines real-world decisions. A construction manager in Austin planning a 16-week build who uses NETWORKDAYS instead of calendar days avoids a costly overrun. For anyone counting weeks, the choice of method — rounding down, rounding up, or keeping decimals — is the difference between an accurate timeline and a misleading one.

Frequently asked questions