Pregnancy Due Date & Gestational Age Calculator
Estimate your due date and how far along you are, five different ways.
The baby can open and close their hands. Reflexes are developing, and kidneys are producing urine.
Trimester Progress
Pregnancy Timeline & Clinical Milestones
Different situations call for different ways of dating a pregnancy, so this calculator offers five. Whether you know the date of your last period, your conception or IVF transfer date, an ultrasound measurement, or an already-estimated due date, it works out your estimated due date, how far along you are in weeks and days, your current trimester, and a countdown — plus a week-by-week size comparison and a milestone timeline. It all runs in your browser.
The five dating methods
Each method reflects the standard clinical approach for that starting point:
LMP: due date = last period + 280 days (adjusted for cycle length)
The last-menstrual-period method follows Naegele's rule, tuning the 280 days for cycles longer or shorter than 28. The conception method counts 266 days from conception; IVF uses the transfer date with an adjustment for a 3-day or 5-day embryo; the ultrasound method rebuilds dates from the gestational age a scan measured; and the reverse method starts from a due date you already have. Gestational age is always counted from the last period, which is why it runs about two weeks ahead of the conception date.
Why a due date is only an estimate
Only about one in twenty babies actually arrives on the estimated due date — most births happen in the weeks around it, and a full-term delivery spans roughly 37 to 42 weeks. Cycle irregularity, uncertain dates, and natural variation all shift the real timing, and an early ultrasound is generally the most reliable way to date a pregnancy. The fetal size comparisons and milestones here are typical averages for interest and reassurance, not a diagnosis. Your healthcare provider's dating always takes precedence.
Frequently Asked Questions
Which method is the most accurate?
An early ultrasound is usually considered the most reliable, especially if your cycles are irregular or you're unsure of your last period. Where methods disagree, your provider's dating — often based on a scan — is the one to follow.
Why is gestational age about two weeks more than time since conception?
By convention gestational age is measured from the first day of your last menstrual period, which is roughly two weeks before conception. So at conception you're already counted as about two weeks pregnant.
Will my baby arrive on the due date?
Probably not exactly. Only around 5% of babies are born on their due date; most arrive in the surrounding weeks, and anything from about 37 to 42 weeks is considered full term.
Is this medical advice, and is my data saved?
It is not medical advice — it's an educational estimate, and prenatal care decisions should be made with your healthcare provider. Nothing you enter is saved; the calculation runs entirely in your browser.