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Gestational Age Calculator

Gestational age in weeks and days from your LMP, due date or conception date, with trimester and EDD.

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Biological Age CalculatorEstimate your biological age from lifestyle factors — fitness, diet, sleep, stress and more. Educational, not medical.Baby Growth Percentile CalculatorWeight, length and head circumference percentiles from the WHO Child Growth Standards, 0-24 months.Baby Milk Intake CalculatorBottle volumes per feed and per day by your baby's weight and age, with the feeding interval.hCG Doubling Time CalculatorCompute the doubling time and percentage rise between two hCG results, read against the expected range for the level reached.Implantation CalculatorDate the 6-to-12-day implantation window from your last period or a known ovulation date, with the peak days, the earliest reliable test date and the expected period.IVF Due Date CalculatorDate an IVF pregnancy from the transfer date and the embryo's age, with gestational age today, the trimester and term milestones, and the equivalent LMP date.Menstrual Cycle CalculatorPredict your next periods, ovulation day, fertile window and current cycle phase from your last period.Menstrual Cycle Length CalculatorAverage cycle length, shortest, longest and regularity from your recent period start dates.

Gestational Age Calculator works straight from this page — free, instant, nothing to install. Its place is under Pregnancy & baby; Biological Age Calculator and Baby Growth Percentile Calculator answer the questions closest to this one.

How to use it

  1. Open the tool — no signup or install needed.
  2. Enter your input or adjust the available options.
  3. Get your result instantly, then copy or download it.

Frequently asked questions

What is Gestational Age Calculator?

Gestational age in weeks and days from your LMP, due date or conception date, with trimester and EDD.

When would I actually use this?

Placing a pregnancy on the calendar: the estimated due date, the current week, and when the usual appointments and screenings fall.

What is the most common mistake?

Reading the due date as a deadline. It is a median: fewer than one birth in twenty happens on it, and a normal term spans several weeks around it.

How is Gestational Age Calculator different from Biological Age Calculator?

They sit next to each other but answer different questions: Biological Age Calculator is the one to open when you need it to estimate your biological age from lifestyle factors — fitness, diet, sleep, stress and more. Educational, not medical. Pick whichever matches what you're starting from — both are free.

Is there a tool for the next step?

Baby Growth Percentile Calculator is the closest one after this: Weight, length and head circumference percentiles from the WHO Child Growth Standards, 0-24 months.

What else is worth having open alongside it?

Baby Milk Intake Calculator and hCG Doubling Time Calculator — they come up in the same task often enough to be worth a second tab.

Where do the figures come from?

Dating follows Naegele's rule (280 days from the last period) or the transfer date for assisted conception. An early ultrasound is more accurate than any calculation and takes precedence over it.

Further reading

All guides →
ExplainerHow Pregnancy Dating Actually WorksGestational age is counted from your last period, about two weeks before conception, so a pregnancy of 6 weeks contains an embryo of about 4 weeks. Here is Naegele's rule derived, the correction for a cycle that is not 28 days, and when ACOG says an early scan should replace your dates.ExplainerIVF Dating Is the One Case Where the Date Is Actually KnownEvery other pregnancy is dated from an estimate. After IVF, fertilisation is timed to the hour, so gestational age is arithmetic: 266 days from fertilisation, minus the embryo's age at transfer. Here is the derivation for day-3, day-5 and day-6 embryos, why frozen and fresh transfers use the same rule, why an early scan rarely moves an IVF date, and what the two-week offset on a scan report means.ExplainerhCG Doubling Time, and What a Single Number Cannot Tell YouDoubling time is ln(2) times the interval divided by the natural log of the ratio. Here it is derived and worked on real pairs, with the two things most often got wrong online: the expected rate slows as the level rises, and a single value is meaningless because the reference range at one gestational week can span more than two hundredfold.ExplainerImplantation Timing and the Window That Decides a Test ResultHow early you can test is the sum of three delays: when implantation happens, how fast hCG climbs from that moment, and what the test can detect. Each one is measured in the literature, so the chain can be computed end to end — and it explains exactly why an early negative is so often wrong.ExplainerCycle Length, Ovulation, and What a Fertile Window Really IsOvulation is estimated far better by counting backwards from the next period than forwards from the last one, because the phase after ovulation is the stable one. Here is the inversion worked for every cycle length, the fertile window from the study that defined it, and the failure rates that make this unusable as contraception.GuidePregnancy Week by Week: The Calendar and What Each Stage MeansPregnancy is counted in 40 weeks from your last period, not from conception — so you are already two weeks pregnant at conception. Here is the full calendar, the trimester boundaries and what term actually means.