Generic selectors
Exact matches only
Search in title
Search in content
Post Type Selectors
page
Gestation calculator icon showing a pregnant figure silhouette and clock

Gestation Calculator

Gestation Calculator

Estimate a due date and track progress for humans or animals

Saved Calculations
No saved calculations yet.

Pick a species, then enter either the first day of the last period (humans only) or the conception/mating date. The calculator adds the average gestation length for that species to estimate a due date, and shows how far along the pregnancy is right now.

Human estimates use the standard 280-day (40-week) LMP convention, or 266 days from conception. Animal estimates use typical average gestation lengths for that species — actual timing varies naturally around the average.

This is an estimate only, not a diagnosis. Talk to a doctor or veterinarian for guidance specific to your situation.

A gestation calculator estimates when a pregnancy is due and how far along it currently is, based on either the first day of the last menstrual period (for humans) or the mating or conception date (for animals). This tool covers humans and a range of common animal species, each using that species’ typical average gestation length.

How to use this gestation calculator

  1. Choose a species from the dropdown — human, dog, cat, horse, cow, and other common animals are included.
  2. Enter the first day of the last period (humans) or the mating/conception date (animals).
  3. The calculator adds that species’ average gestation length and shows the estimated due date and current progress.

How the due date is estimated

Due Date = Start Date + Average Gestation Length (species-specific)

Human due dates traditionally use the 280-day (40-week) convention counted from the last menstrual period, or 266 days if counted from conception. Each animal species has its own typical average — a dog’s is around 63 days, for example — and the calculator swaps in the right figure automatically based on your species selection.

Why the result is an estimate, not a guarantee

Actual gestation length varies naturally around the average for every species, including humans. Full-term human pregnancies routinely span anywhere from about 38 to 42 weeks and still fall within the normal range. This calculator gives you the statistically expected date, not a fixed prediction — always confirm timing with a doctor or veterinarian.

Frequently asked questions

Should I use the last period date or the conception date for humans?

Either works, but they use slightly different day counts — 280 days from the last menstrual period, or 266 days from conception — since ovulation typically occurs about two weeks after the period starts. Pick whichever date you know more reliably.

Why is my due date different from what my doctor told me?

Doctors often adjust the estimate using ultrasound measurements, which can be more accurate than a calendar-based calculation, especially if your cycle isn’t exactly 28 days. Use this calculator as a general estimate, not a replacement for medical dating.

Does this work for pets and farm animals?

Yes. The species dropdown includes common pets and livestock, each using that animal’s typical average gestation length, so you get a due-date estimate appropriate to the animal you selected.