Weeks to Months Calculator

Calendar Chronometry & ACOG Obstetric Standards

The American College of Obstetricians and Gynecologists (ACOG) defines full-term pregnancy as 40 gestational weeks (280 days), which equals 9 calendar months + 1 week (or 10 four-week lunar months).

Primary Conversion Formulas

• Standard Calendar Months: Months = Weeks × 730.4375 = Weeks4.3482

• Pregnancy Lunar Months: Lunar Months = Weeks4.0

• Total Days: Days = Weeks × 7

• Total Hours: Hours = Weeks × 168

Pregnancy Trimester Schedule

• First Trimester: Weeks 1 to 13 (0 - 3 months)

• Second Trimester: Weeks 14 to 27 (3 - 6 months)

• Third Trimester: Weeks 28 to 40

How to Use This Calculator

Enter your Number of Weeks (e.g. 24.0 in weeks), Conversion Standard — choose from Standard Calendar Months (1 Month = 4.348 Weeks / 30.44 Days), Pregnancy / Gestational Months (1 Month = 4.0 Weeks / 28 Days), and Starting Date (Optional YYYY-MM-DD) (e.g. 2026-08-15). Results update instantly as you type — adjust any value to compare scenarios.

The Formula

Formula Reference: Weeks to Months Calculator

Input variables:

weeksInput — Number of Weeks

conversionStandardSelect — Conversion Standard

startDateOptional — Starting Date (Optional YYYY-MM-DD)

Computed outputs:

decimalMonthsResult — Total Decimal Months

monthsAndDaysBreakdown — Months & Days Breakdown

totalDaysEquivalent — Total Equivalent Days

pregnancyTrimesterStatus — Pregnancy Trimester Status

totalHoursEquivalent — Total Hours

Mathematical relationships extracted from calculation logic:

totalDays = w * 7

totalHours = totalDays * 24

remD = Math.round((decMonths - fullM) * 28)

Reference constants:

daysPerMonth = 30.4375

Standard: NIST Handbook 44 and BIPM SI unit definitions

Worked Example

At 24 weeks of pregnancy, you are 5.5 calendar months pregnant (or exactly 6.0 lunar months) in the heart of your second trimester.

Understanding Your Result

Unit conversion precision: round to the same number of significant figures as your original measurement. Converting 6 feet to meters gives 1.8288 m — but if your measurement was approximate (±1 inch), expressing more than 2 decimal places is false precision. For international trade and technical specifications, SI units (meters, kilograms, liters) are the standard. US customary units (feet, pounds, gallons) differ from Imperial UK units: 1 US gallon = 3.785 L vs. 1 UK gallon = 4.546 L.