Pregnancy Week Calculator

Professional gestational-age calculator: supports LMP, ovulation day, ultrasound, IUI, IVF and more. Automatically calculates current week, due date, fetal development and prenatal schedule. One-stop week-by-week management for natural-conception and IVF moms.

Calculate Now Features

Accurate Gestational Week Calculation

Choose your conception method and known info, the system will give the most accurate week and professional guidance

Affects full-term standard & check-up density
For risk assessment & personal advice (optional)
Default 28 days, 21-45 days are normal
Select the first day of your last period
System gives a possible range if uncertain
Strong positive OPK day or monitored ovulation
Ultrasound is the most accurate
The day the scan was performed
weeks
Decimal allowed, 8+3 days = 8.4 weeks
mm
Most accurate in early scans; system can auto-calculate
Trans-vaginal is more accurate early on
The day of the insemination
Stimulated cycles have better ovulation control
The day of the embryo-transfer procedure
Blastocysts are 2 days older than cleavage embryos
Fresh/frozen does not affect week calculation
Refer to your procedure record

Pregnancy Week Quick Reference

Baby size, mom changes and check-up items at a glance

1st Trimester (Weeks 1-12)
Week Baby Size Mom Changes Check-up Items
Week 4 Poppy seed Possible implantation bleed Serum hCG
Week 8 Grape Morning sickness peaks Heartbeat scan
Week 12 Plum Nausea eases NT scan
2nd Trimester (Weeks 13-28)
Week Baby Size Mom Changes Check-up Items
Week 16 Avocado Light fetal movement Quad test / NIPT
Week 20 Banana Clear fetal movement Anomaly scan
Week 24 Corn May have leg cramps OGTT diabetes screen
3rd Trimester (Weeks 29-40)
Week Baby Size Mom Changes Check-up Items
Week 32 Pumpkin May have edema Non-stress test
Week 36 Papaya Pack hospital bag Weight estimation scan
Week 40 Watermelon Watch for labor signs Labor assessment
Multiple Pregnancy Notes
  • Twins are full-term at 37 weeks, check-ups are more frequent than singletons
  • Ultrasound every 2 weeks after 28 weeks to monitor growth discordance
  • Consider hospital admission after 34 weeks to reduce travel risks
  • Elective delivery at 36-37 weeks to lower in-utero risks

Why Choose PreMami Pregnancy Week Calculator?

All Conception Methods Covered

Natural, ovulation day, ultrasound, IUI, IVF – whatever your path, we have the right algorithm

Smart & Accurate Algorithms

Built on international OB-GYN standards, CRL/BPD supported, margin ≤ 3 days in early pregnancy

Multiple Pregnancy Specialist

Auto-identifies twins/triplets, 37-week full-term reminder, smarter check-up density

Auto Prenatal Schedule

Personalized check-up timetable generated from your week, with early reminders for key visits

Pregnancy Week Calculator FAQ

Medically, gestational age starts from the first day of your last menstrual period (LMP), not the conception day. Most women can recall their period date accurately, while ovulation and fertilization dates are usually uncertain. A full pregnancy is 40 weeks (280 days).

If your cycles are irregular, use an early ultrasound (6-8 weeks) to measure crown-rump length (CRL) – the most accurate method. Our calculator lets you enter the gestational weeks shown on the scan, and the system will back-calculate your LMP and due date automatically.

Early ultrasound (≤ 12 weeks) is the gold standard; a discrepancy ≤ 7 days is normal. If the difference is > 7 days, adjust your due date according to the scan. Late ultrasounds have larger errors due to individual fetal size variation.

IVF pregnancies are dated from the transfer day: add 263 days for day-3 embryos, 261 days for day-5 blastocysts, 260 days for day-6 blastocysts. Select IVF mode in our calculator and the correct algorithm is applied automatically.

7 days = 1 week. Example: 35 days = 5 weeks 0 days; 38 days = 5 weeks 3 days. Our calculator auto-converts and displays “weeks + days” format, which is standard in obstetrics.

Calculation method is the same, but full-term is different: twins are full-term at 37 weeks (vs. 40 for singletons). Check-ups are also more frequent: every 3-4 weeks before 28 weeks, every 2 weeks until 36 weeks, then weekly.

Our tool uses international OB-GYN standards; early-ultrasound-based calculations have an error ≤ 3 days. Always confirm your gestational age with your obstetrician, especially if cycles are irregular or you had assisted reproduction.

First-time moms usually feel quickening at 18-20 weeks; moms who have given birth before may feel it as early as 16-18 weeks. Slim mothers tend to feel movements earlier than plus-size mothers. If you feel nothing by 24 weeks, contact your doctor.