Evidence-based pregnancy and fertility calculators
Pregnancy calculator: due date, ovulation and gestational age
Pregnancy calculators to estimate your due date, fertile window and week of pregnancy, using the methods published by ACOG, NICE and the Institute of Medicine. Every result shows the formula used, its source and the range of uncertainty around it, and states where US and UK guidance differ.
Published clinical methods
Each calculation follows an ACOG, NICE or IOM method, and the source is cited beside the result.
No account needed
You do not need an account, and we do not save the details you enter into a calculator.
US and UK guidance
Units, date formats and guidance follow the region you select, and differences between the two are stated.
The method is shown
Every result states the formula it came from and the evidence behind it.
The calculators
Due date
Estimate your due date from your last period, conception, an ultrasound scan or an IVF transfer, with the likely range around it.
CalculateOvulation & fertile window
Estimate your fertile window and ovulation date from the length of your cycle.
CalculatePregnancy week
Calculate how many weeks and days pregnant you are today, and which trimester you are in.
CalculateConception date
Estimate when conception most likely took place from a due date or an ultrasound scan, given as a range of dates.
CalculateIVF due date
Calculate an IVF due date from the transfer date and the age of the embryo at transfer.
CalculatePregnancy test calculator
Find the earliest date a home pregnancy test gives a reliable result after ovulation.
CalculatePregnancy weight gain
The recommended total weight gain in pregnancy for your pre-pregnancy BMI, with the NICE position for the UK.
CalculatePeriod & cycle predictor
Predict your next periods and the fertile window in each cycle.
CalculateTrying to conceive
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Cycles and ovulation
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Male fertility
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Preparing for pregnancy
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Early pregnancy
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Every result can be checked against its source
Each calculator names the formula it uses and the guideline it comes from. Where the evidence is limited, the result says so rather than implying more certainty than exists.
- ACOG American College of Obstetricians and Gynecologists
- NICE National Institute for Health and Care Excellence
- IOM Institute of Medicine, now the National Academy of Medicine