Every pregnancy date, checked against every anchor you actually know
Most calculators ask for one date and silently assume a 28-day cycle. ExpectCalc dates your pregnancy from every anchor you can provide — last period, cycle length, ovulation, conception, ultrasound, IVF transfer date — and shows you where the methods agree, where they disagree, and by how much.
- 100% free, no sign-up
- Runs in your browser — no data leaves your device
- ACOG / IOM primary sources on every page
- IVF & FET dating built in
Calculators
Pregnancy Due Date Calculator
Enter whatever you actually know — last period, ovulation test date, when you conceived, an early ultrasound, or your IVF transfer date — and this calculator estimates your due date with each method side by side, so you can see how much the answers really differ.
Most usedOvulation Calculator
Tell us the first day of your last period and how long your cycle usually runs.
Trying to conceiveIVF Due Date Calculator
IVF pregnancies are the easiest to date precisely — the exact day of fertilization is known.
IVF & FETConception Date Calculator
Estimate the day you conceived from your due date or your last period — with a full six-day window and the three days that carry most of the probability.
DatingImplantation Calculator
Enter your ovulation day (or your last period and cycle length) to get your implantation window, the three most likely days inside it, and the earliest date a test could turn positive.
Two-week waitBeta hCG Doubling Time Calculator
Enter your quantitative beta hCG values and the dates they were drawn.
Blood testsPregnancy Weight Gain Calculator
Based on the Institute of Medicine 2009 guidelines — the reference used by ACOG — this calculator gives your total recommended gain, the weekly rate for the second and third trimesters, how much you should have gained by your current week, and how much is left.
Prenatal healthWeeks to Months Pregnant Converter
Type your week number (or your due date) and instantly see which month you are in, your trimester, how many days remain, and the full conversion chart from 4 to 42 weeks.
ConversionWeek-by-week guides
6 Weeks Pregnant
Baby is about the size of a lentil — development, symptoms, and this week's checklist.
Week by week12 Weeks Pregnant
Baby is about the size of a lime — development, symptoms, and this week's checklist.
Week by week20 Weeks Pregnant
Baby is about the size of a banana — development, symptoms, and this week's checklist.
Week by week28 Weeks Pregnant
Baby is about the size of an eggplant — development, symptoms, and this week's checklist.
Week by week34 Weeks Pregnant
Baby is about the size of a cantaloupe — development, symptoms, and this week's checklist.
Week by week38 Weeks Pregnant
Baby is about the size of a leek — development, symptoms, and this week's checklist.
Week by weekWhy your "last period" date can be two weeks wrong
Implantation bleeding, cycle-length corrections, and when a dating ultrasound settles the question.
GuideFrom the blog
How Far Apart Are Dating Methods, Really? — Same last period, three dating formulas, six cycle lengths: our engine puts due dates 8 to 12 days apart, and a two-week LMP error shifts them 14 days.
IVF Due Date: Day-3 vs Day-5 Transfer — One formula — transfer date plus 266 days minus embryo age — covers fresh, frozen, and retrieval dating, with worked day-3/5/6 and retrieval-only examples.
Why cross-checking matters
Pregnancy dating is treated online as if it were arithmetic with one right answer. In practice it is measurement with error bars: the last-period method assumes a cycle you may not have, ovulation-tracking gives a sharp but narrow window, ultrasound drifts as pregnancy advances, and IVF dates are exact but only exist for a minority of pregnancies. When two honest methods disagree by nine days, a tool that shows you one number is choosing for you.
Every calculator here is built around the same idea — take every anchor, compute each one independently, and display the spread. Where the spread is small, you have a confident answer. Where it is large, you have the exact argument for asking your provider for a dating ultrasound before 14 weeks, while it can still settle the question.
What makes these calculators different
Cycle length is a first-class input, not a hidden 28-day assumption. Implantation, conception, and IVF pages use the biological 266-day length from fertilization rather than reusing period-based math. hCG interpretation applies level-dependent bands instead of one universal doubling rule. And every page lists the primary sources — ACOG, IOM, the original studies — so the numbers can be audited rather than trusted.
Nothing here requires an account, an email address, or an app install. The calculators run entirely in your browser; the pages work printed; and the medical disclaimer travels with every result.