For educational and reference use only. These calculators do not replace clinical judgement, local protocols, or a qualified clinician. Verify every result independently before it informs patient care.
Women's & obstetric imaging
Gestational Age & EDD (CRL)
Gestational age and estimated due date from the crown–rump length using the Robinson–Fleming equation. The most accurate dating method in the first trimester (BMUS dating table: CRL 5–80 mm).
Defaults to today if left blank.
Result
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Enter all values to calculate.
Formula
GA (days) = 8.052 × √(CRL × 1.037) + 23.73, CRL in mm (Robinson–Fleming, as printed by BMUS 2009). EDD = scan date + (280 − GA).
References
- Robinson HP, Fleming JE. A critical evaluation of sonar "crown-rump length" measurements. Br J Obstet Gynaecol 1975;82(9):702–710.
- Loughna P, Chitty L, Evans T, Chudleigh T. Fetal size and dating: charts recommended for clinical obstetric practice. Ultrasound 2009;17(3):161–167 (BMUS). Prints the equation with the 1.037 factor; Appendix 1 Table 1 is the dating table, 5 mm (6+0) to 80 mm (13+6).
- ACOG/AIUM/SMFM Committee Opinion 700: Methods for Estimating the Due Date (2017).
Disclaimer
BMUS 2009 dates from CRL of 5 mm (6+0 weeks) to 80 mm (13+6 weeks). Its Appendix 1, Table 1, and recommends head circumference beyond that. Use head/ biometry-based dating. Measure CRL in a true mid-sagittal plane, neutral fetal position. NHS FASP offers combined screening only where the CRL is 45.0–84.0 mm; above 84.0 mm it dates from head circumference and offers the quadruple test at HC ≥ 101.0 mm. The equation’s range and the screening window are not the same thing.
For educational and reference use only. These calculators do not replace clinical judgement, local protocols, or a qualified clinician. Verify every result independently before it informs patient care.
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