Gestational Age

Estimates gestational age from weeks and days.

Obstetrics & Gynecology ObstetricsEvidence-BasedUpdated 2026-07

Clinical decision-support tool for qualified healthcare professionals. Results are not a diagnosis and should not replace professional clinical judgment.

Clinical Notes

Gestational age is commonly used for pregnancy dating and fetal growth assessment.

Calculator Information

Specialty

Obstetrics

📋 Reference Ranges

Normal Range

0–42 weeks

What This Calculator Measures

Calculates gestational age in decimal weeks from entered weeks and days, and relates this to the weeks + days format clinicians commonly use in pregnancy.

How to Use

Enter the gestational age in completed weeks and days (e.g., 32 weeks 3 days).
The calculator returns gestational age as a decimal number of weeks (weeks + days/7).
Clinicians commonly express the same age as '32 weeks 3 days'; the decimal output (32.43 weeks) is the equivalent single number.
Clinical dating of pregnancy typically relies on the LMP or, when available, established ultrasound dating.

How the Calculation Works

Gestational age = weeks + days / 7, expressed in weeks with the days as the fractional remainder.

Variables Explained

Weeks

Completed weeks of gestation.

Days

Additional days beyond the completed weeks, divided by 7.

Interpretation Guide

The calculator returns gestational age in decimal weeks; for example, 32 weeks 3 days is reported as approximately 32.43 weeks. Clinically, gestational age is usually expressed in completed weeks plus days (e.g., 32w3d), and this decimal value is the mathematical equivalent. The calculator does not determine viability or obstetric diagnosis — that requires full clinical and ultrasound assessment.

Pregnancy-specific

Clinical Significance

Gestational age is the cornerstone of pregnancy dating and fetal growth assessment; expressing it consistently as weeks plus days (or a decimal equivalent) supports accurate documentation and interpretation of prenatal milestones.

When It Is Useful

Converting a weeks + days gestational age into a decimal number of weeks
Educational review of gestational age reporting
Supporting documentation and calculations that require gestational age in weeks

When It Is Not Useful

To determine pregnancy viability or fetal well-being
To replace ultrasound-based dating when dating is uncertain
As a substitute for clinical assessment or obstetric diagnosis

Common Mistakes

Entering 7 or more days in the days field instead of carrying the excess into weeks, even though the accepted range for days is 0 to 6.
Interpreting the decimal remainder as a day count, when the fractional part represents a portion of a week and the value is simply the entered weeks and days expressed differently.
Expecting the tool to derive gestational age from the last menstrual period date or ultrasound measurements, since it only converts an already determined weeks-plus-days age into decimal weeks.

Limitations

The calculator is a unit conversion (weeks + days/7); it does not compute gestational age from dates or from ultrasound measurements.
Accuracy of the entered age depends on how pregnancy dating was established (LMP or ultrasound).
The decimal output (e.g., 32.43 weeks) should not be mistaken for a new clinical estimate; it is the same age expressed differently.
The calculator accepts 0–42 weeks and 0–6 days, matching its input limits.

Worked Example

A patient's gestational age is 32 weeks and 3 days.

Inputs:

weeks: 32

days: 3

Expected Result: Gestational age = 32 + 3/7 ≈ 32.43 weeks (32 weeks 3 days).

Evidence & References

Source:: ACOG Committee Opinion
Content updated:: 2026-08

ACOG Committee Opinion No. 700. Obstet Gynecol. 2017;129(5):e150-e154.

References

ACOG Committee Opinion No. 700: Methods for estimating the due date. Obstet Gynecol. 2017;129(5):e150-e154. (Clinical guideline)

Frequently Asked Questions

How do I convert decimal weeks back to weeks and days?

Take the whole number as completed weeks, then multiply the decimal remainder by 7 to recover the days. For example, 32 weeks 3 days is expressed as approximately 32.43 weeks, so multiplying that remainder by 7 returns about 3 days. Clinically the age is usually reported as completed weeks plus days, such as 32w3d, rather than as a decimal.

Does this calculator establish the gestational age for my patient?

No. It converts an age you have already determined from weeks and days into decimal form; it does not compute gestational age from the LMP date or from ultrasound biometry. The accuracy of the entered age depends entirely on how the pregnancy was dated, and the decimal output is the same age expressed differently, not a new clinical estimate.

Why are the input limits 0-42 weeks and 0-6 days?

These limits match the ranges clinicians use when documenting gestational age: days are counted 0 to 6 because a seventh day becomes one additional week, and 42 weeks covers the post-term range. Values outside these ranges usually indicate a data-entry error rather than a true gestational age.

Disclaimer: This calculator is intended for educational and clinical decision support purposes only. Gestational age reflects the entered dating only and does not determine pregnancy viability or obstetric diagnosis.