Ovulation
Ovulation is estimated at about 14 days before your next expected period. The fertile window covers the 5 days before ovulation and the day of ovulation. Irregular cycles make this less reliable.
Free & private tools
Fertility Calculators
Estimate your fertile window, due date or BMI, and check when it may be time to see a specialist. Quick, simple, and nothing you enter is saved or sent.
- No sign-up
- Nothing stored
- Reviewed guidance
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Fertile window6 days
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Pregnancy40 weeks
Ovulation calculator
Estimate your most fertile days based on your cycle.
2140 days
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Enter the first day of your last period to see your estimated fertile window.
Pregnancy due date calculator
Estimate your due date and how far along you are.
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Your estimated due date, current week and trimester will appear here.
IVF due date calculator
After IVF, the due date is based on your embryo transfer date and embryo age.
Embryo age at transfer
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Enter your transfer date to see your estimated due date.
BMI calculator
Body mass index is one general measure your doctor may consider when planning fertility treatment.
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Enter your height and weight to see your BMI.
Should I see a fertility specialist?
Based on general guidance about age and how long you've been trying.
Anything else that applies? (optional)
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Enter your age and how long you've been trying to see general guidance.
All calculations happen on your device. Nothing you enter is saved or sent to us.
Calculators estimate. Doctors evaluate.
Want answers based on your own body?
A consultation can check ovulation, hormones and other factors that no calculator can measure.
Behind the numbers
How these calculators work
Each tool uses standard, widely used estimates. They're a helpful starting point, not a diagnosis.
Due date
Pregnancy is counted as 40 weeks (280 days) from the first day of the last period, adjusted for cycle length. Your doctor may update the date after an early ultrasound.
IVF due date
Uses the embryo transfer date: 261 days after a day-5 transfer, or 263 days after a day-3 transfer. Your fertility team will confirm your dates.
BMI
Weight in kilograms divided by height in metres squared, using WHO categories. BMI doesn't measure body composition, so it's only one general indicator.
Specialist timing
General guidance suggests evaluation after 12 months of trying if under 35, after 6 months if 35 or older, and sooner if over 40 or with known risk factors.
Important
These tools are not contraception and can't confirm ovulation, pregnancy or infertility. For irregular cycles or health concerns, please speak with a doctor.
How accurate is an ovulation calculator?
It gives an estimate based on average cycle patterns. Ovulation timing can vary from cycle to cycle, especially if your periods are irregular. Ovulation tests, cycle tracking or monitoring by your doctor can give more information.
Can I use the ovulation calculator to avoid pregnancy?
No. These estimates are not reliable enough to be used as contraception. Please speak with a doctor about suitable contraception.
My cycles are irregular. Can I still use these tools?
You can, but results will be less reliable. Irregular or absent periods can be a sign of an ovulation problem, so it's worth discussing with a doctor. Read about PCOS / PCOD.
Why might my doctor give a different due date?
An early pregnancy ultrasound can measure the baby's development directly, which may give a more accurate estimate than dates alone. Your doctor will tell you which date to use.
Does BMI affect fertility treatment?
Weight can be one of several factors your doctor considers when planning treatment. It's best discussed individually; your doctor may offer lifestyle guidance where appropriate.
Helpful next steps