Pregnancy Calculator
Estimate your due date, current week and trimester, and fetal size from your last period, conception date, IVF transfer, or ultrasound.
Estimated Due Date
January 31, 2027
Summary
Based on a last period date of April 26, 2026, the estimated due date is January 31, 2027 — currently 10 weeks and 0 days along (25% complete), in the first trimester, with the baby about the size of a strawberry.
Current Week
10 w 0 d
Trimester
1 of 3
Weeks Remaining
30
Pregnancy progress
25.0%
complete
Baby is about the size of a strawberry.
What is a Pregnancy Calculator?
A pregnancy calculator estimates your due date and current gestational age from whichever dating information you have — the first day of your last menstrual period, a known conception date, an IVF embryo transfer date, or an early ultrasound. Childbirth usually occurs about 38 weeks after conception, or roughly 40 weeks after the last menstrual period, since ovulation and conception typically happen about two weeks after a period begins.
The World Health Organization defines a normal pregnancy term as 37 to 42 weeks. Research shows fewer than 4% of babies are born on their exact due date — about 60% arrive within a week of it, and nearly 90% within two weeks — so treat the due date as an estimate and a planning anchor, not a prediction.
Your Trimester Calendar
| Trimester | Starts | Ends |
|---|---|---|
| First Trimester (current) | Apr 26, 2026 | Jul 25, 2026 |
| Second Trimester | Jul 26, 2026 | Oct 31, 2026 |
| Third Trimester | Nov 1, 2026 | Jan 31, 2027 |
Key Milestones
| Milestone | Week | Date |
|---|---|---|
| End of First Trimester | 13 | Jul 26, 2026 |
| Anatomy Scan (~Week 20) | 20 | Sep 13, 2026 |
| Viability (~Week 24) | 24 | Oct 11, 2026 |
| Third Trimester Begins | 28 | Nov 8, 2026 |
| Full Term (Week 37) | 37 | Jan 10, 2027 |
| Estimated Due Date | 40 | Jan 31, 2027 |
How Due Dates Are Calculated
Regardless of the dating method, this calculator assumes a standard 280-day (40-week) pregnancy from the start of gestation. The methods differ only in how that start point is determined:
- Last period (Naegele's rule): due date = last period date + 280 days, adjusted for cycles longer or shorter than 28 days.
- Conception date: due date = conception date + 266 days (38 weeks).
- IVF transfer: due date = transfer date + 266 days, minus the embryo's age at transfer (3 or 5 days).
- Ultrasound: due date = scan date + (280 days − gestational age measured at the scan).
Which Method Is Most Accurate?
A first-trimester ultrasound (ideally between 8–13 weeks) is generally considered the most accurate dating method, since fetal measurements are highly consistent across pregnancies at that stage. A known conception or IVF transfer date is similarly precise. The last-period method is the least precise of the four, since it assumes ovulation always occurs exactly 14 days after a period starts — not true for everyone, especially with irregular or non-28-day cycles.
Why Trimesters Matter
Each trimester carries distinct screening recommendations and typical symptoms. The first trimester (weeks 1–13) is when most miscarriages occur and when neural tube and organ development is most sensitive to teratogens, making prenatal vitamins with folic acid especially important early on. The second trimester (14–26) includes the detailed anatomy ultrasound and is often when energy levels improve. The third trimester (27–40) is when the fetus reaches viability and gains most of its birth weight, and when appointments become more frequent to monitor for complications like preeclampsia.
Pregnancy Weight Gain and Prenatal Care
For a person starting pregnancy at a normal BMI, 25–35 pounds of total weight gain is the commonly cited target, distributed differently across trimesters (least in the first, most in the second and third). Recommended targets differ for underweight, overweight, and multiple (twin/triplet) pregnancies — see the Pregnancy Weight Gain Calculator for a personalized range. Regular prenatal visits, an ultrasound-confirmed due date, and standard blood and glucose screening are all part of routine care regardless of which method you use to estimate your due date.
Example — Your Current Inputs
Based on a last period date of April 26, 2026, the estimated due date is January 31, 2027 — currently 10 weeks and 0 days along (25% complete), in the first trimester, with the baby about the size of a strawberry.
Additional Example — Dating by Ultrasound
An ultrasound performed on March 1 measures the fetus at exactly 10 weeks 0 days. Working backward, gestation is estimated to have started on December 21 (70 days before the scan), and adding the full 280-day term gives a due date of September 26 — regardless of what the last-period date would have suggested. Because ultrasound measurements are so consistent in early pregnancy, doctors will typically use the ultrasound-based due date over the LMP-based one whenever the two disagree by more than about a week.
About These Parameters
- Last Period Date & Cycle Length
- The first day of your most recent period, plus your typical cycle length. A 28-day cycle is the textbook assumption; entering your actual average cycle length shifts the estimate to better match when you likely ovulated.
- Conception Date
- The specific date fertilization is believed to have occurred, if known — for example from ovulation predictor kits or basal body temperature tracking.
- IVF Transfer Date
- The date an embryo was transferred during IVF, along with whether it was a day-3 (cleavage-stage) or day-5 (blastocyst-stage) embryo — this offsets how many days before transfer conception effectively occurred.
- Ultrasound Date & Gestational Age at Scan
- The date of an ultrasound and the gestational age (in weeks and days) the sonographer measured at that scan — found on your ultrasound report. This is often the most reliable dating method available.
Frequently Asked Questions
Why did my due date change after an ultrasound?
Because the last-period method assumes a textbook 28-day cycle with ovulation on day 14, which doesn't apply to everyone. An early ultrasound directly measures the fetus, so doctors typically adjust the due date to the ultrasound estimate if it differs from the LMP-based one by more than about 5–7 days in the first trimester.
How accurate is a home pregnancy test?
Home urine tests can detect pregnancy hormone (hCG) as early as the day of a missed period for many brands, with accuracy improving the longer you wait. A clinical blood test at a doctor's office is more sensitive and can sometimes detect pregnancy 6–8 days after fertilization, before a period would even be due.
Is it normal to go past my due date?
Yes — only about 4% of babies are born exactly on their due date, and full term is defined as any birth between 37 and 42 weeks. Most care providers begin closer monitoring past 40–41 weeks and discuss induction options if labor hasn't started by 41–42 weeks.
What's the difference between day-3 and day-5 embryo transfers?
A day-3 embryo (cleavage stage) is transferred earlier in development than a day-5 embryo (blastocyst stage). Because a day-5 embryo is 2 days more developed at transfer, the effective conception date is correspondingly earlier relative to the transfer date — this calculator adjusts for that difference automatically based on which option you select.