Pregnancy Calculators
Calculate baby age, baby weight gain and conception and other pregnancy calculations.
Pregnancy dates are all counted from the first day of the last menstrual period, not from conception. These calculators use that starting point to estimate the fertile window, the due date and how far along a pregnancy is, and a few track a baby's first months.
Which Pregnancy calculator do you need?
- When am I most likely to conceive?Ovulation CalculatorEstimates ovulation and the fertile window from your last period and cycle length.
- When is my baby due?Due Date CalculatorAdds 280 days to the first day of your last period (Naegele's rule).
- How many weeks pregnant am I, and which trimester?Pregnancy CalculatorDue date, current week and trimester from one date.
- How much weight should I gain during pregnancy?Pregnancy Weight Gain CalculatorRecommended total gain range for your pre-pregnancy BMI, per Institute of Medicine guidance.
- How old is my baby in weeks and days?Baby Age CalculatorExact age in years, months, weeks and days from the date of birth.
All Pregnancy Calculators
A due date is an estimate
Naegele's rule assumes a 28-day cycle with ovulation on day 14, and most babies are not born on the day it gives. Cycle length changes the likely ovulation date, which is why the ovulation calculator asks for it — and an early ultrasound dating scan is what clinicians use to confirm or adjust the due date.
Limitations
- General estimates, not medical advice; your doctor or midwife's dating takes precedence.
- Irregular cycles make date-based estimates less reliable.
Pregnancy Guides
How a Pregnancy Due Date and Current Week Are Calculated
A pregnancy due date is simply the first day of the last menstrual period plus 280 days — and the current week and trimester follow from counting how many days have passed since that same starting date.
Read guideHow an Ovulation Date and Fertile Window Are Calculated
Ovulation is estimated by counting backward 14 days from the next expected period, since the post-ovulation luteal phase is a relatively fixed length — and a longer overall cycle shifts that ovulation date later, not the 14-day countdown itself.
Read guideHow Baby Weight Gain Rate Is Calculated
Weight gain rate is simply the total gain since birth divided by the baby's age, giving a weekly and daily average — not a percentile assessment.
Read guideHow Conception Date Is Estimated (And How It Differs from the Due Date Calculation)
Conception date is estimated as roughly 14 days after the start of your last menstrual period (LMP), with a several-day fertile window around that point, since ovulation — not the period itself — is what actually determines when conception can occur.
Read guideHow Your Pregnancy Due Date Is Calculated (Naegele's Rule Explained)
The standard due-date estimate is simply the first day of your last menstrual period (LMP) plus 280 days (40 weeks) — a method called Naegele's rule — which counts from before conception actually happens, not from conception itself, which is why "40 weeks pregnant" doesn't mean 40 weeks since conception.
Read guide