Last reviewed:

Health & Fitness

Due Date by Ultrasound (CRL) Calculator

Gestational age and estimated due date from a first-trimester crown–rump length (CRL) measurement, using the Robinson & Fleming (1975) formula.

Your inputs

Change any value, everything updates instantly.

Allowed range 3–85 mm.

Allowed range 0–200 days.

Try an example

Gestational age today

10 weeks 1 days

This means your gestational age today works out to 10 weeks 1 days with the values you entered.

Gestational age today: 10 weeks 1 daysDays until due date: 209 days
Gestational age todayDays until due date
10.2

What you are seeing

Each bar grows to show one result for your everyday situation.

The top bar is the main answer: 10 weeks 1 days.

Change crown–rump length (crl) (now 35) and every bar updates instantly.

Days until due date

209 days

Worked out from your inputs using the formula below.

Estimated due date

May 14, 2027

Worked out from your inputs using the formula below.

Trimester

First

Worked out from your inputs using the formula below.

Age at scan

10.2 weeks

Worked out from your inputs using the formula below.

Result explanation: Gestational age today

10 weeks 1 days.

Real-life comparison: With crown–rump length (crl) 10% higher, it would be 10.53 .

Low, normal or high? Educational estimate only. Your obstetric provider sets the official due date (ACOG Committee Opinion 700; Robinson & Fleming, Br J Obstet Gynaecol 1975).

Graph and details

3244465850714Crown–rump length (CRL)Gestational age today

How the answer changes with crown–rump length (crl)

How to read this chart: The line shows the main result across the allowed range. The dot marks your input.

What this calculator does

Gestational age and estimated due date from a first-trimester crown–rump length (CRL) measurement, using the Robinson & Fleming (1975) formula.

What your result means

This means your gestational age today works out to 10 weeks 1 days with the values you entered.

Real-life numbers vary, prices, habits and conditions change, so treat this as a practical guide.

Results are shown rounded; the full value is used internally.

The formulas

The same formula runs every time you change an input.

1. Due Date by Ultrasound (CRL)

GA (days) = 8.052 × √CRL(mm) + 23.73; days to due date = 280 − GA

Symbols

crl
Crown–rump length (CRL) (mm)
ago
Days since the scan (days)

Why this formula works

This is the standard everyday arithmetic for this situation, using the values you enter.

Unit check

Inputs are converted to consistent units before calculating ✓

Worked example

  1. Substitute your values: Crown–rump length (CRL) = 35; Days since the scan = 0
  2. Apply the formula: GA (days) = 8.052 × √CRL(mm) + 23.73; days to due date = 280 − GA = 10 weeks 1 days

Common mistakes

  • Entering a value in the wrong unit (for example minutes instead of hours).
  • Using an outdated price or rate.
  • Forgetting extra costs or time that apply in your case.

Working for your numbers

  1. Substitute your values: Crown–rump length (CRL) = 35; Days since the scan = 0
  2. Apply the formula: GA (days) = 8.052 × √CRL(mm) + 23.73; days to due date = 280 − GA = 10 weeks 1 days

This means your gestational age today works out to 10 weeks 1 days with the values you entered.

Frequently asked questions

What does this due date by ultrasound (crl) calculator calculate?

Gestational age and estimated due date from a first-trimester crown–rump length (CRL) measurement, using the Robinson & Fleming (1975) formula.

How accurate is the result?

The calculation follows the stated formula exactly. Your result is an estimate and depends on the accuracy of the values you enter.

Can I use different units or currencies?

Yes. Use the controls beside the calculator inputs. Conversions preserve the underlying value used by the formula.

Symbols and assumptions

crl
Crown–rump length (CRL) (mm)
ago
Days since the scan (days)
  • Values entered are realistic for your situation.
  • Rates and prices stay constant over the period calculated.
  • Displayed values are rounded; internal values are not.

Sources and review

Reviewed 2026-09-25 · Next review 2027-09-25

Time and Frequency DivisionNISTHandbook 44 — specifications for weighing and measuring devicesNIST

Important limitation. Practical estimate for everyday planning. Real outcomes depend on prices, conditions and personal circumstances, check important figures before relying on them.

Quick reference

Due Date by Ultrasound (CRL) Calculator: results for common inputs, worked out with the formula on this page.
ScenarioCrown–rump length (CRL) (mm)Days since the scan (days)Gestational age today
Worked example35010 weeks 1 days
Half the amounts17.508 weeks 1 days
Double the amounts70013 weeks 0 days

Need the full picture? Get the detailed PDF report with charts, tables, formulas and working steps.

Reviewed 2026-10-02 · Next review 2027-10-02

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