Pregnancy Calculator

Track your pregnancy progress by week and trimester. Calculate how far along you are, see upcoming milestones, and countdown to your due date.

Free to use. Runs in your browser.

Track your pregnancy by entering your due date or last period. A full pregnancy is 40 weeks divided into three trimesters.

Enter your information to see your current week, trimester, and upcoming milestones.

Enter Your Information

Your Due Date

Enter your estimated due date as provided by your healthcare provider.

Educational Estimates Only: These calculations are approximations based on population-level formulas and may not accurately reflect your individual health status. Body composition varies significantly due to factors like muscle mass, bone density, hydration, and ethnicity. This is not medical advice. Always consult a qualified healthcare provider for personalized assessment, diagnosis, or treatment decisions.

Methodology and sources

Formula or method

Calculates pregnancy progress from the selected dating input using Naegele-style dating: 280 days from LMP, 266 days from conception, or ultrasound and IVF adjustments back to gestational age.

Basis and assumptions

Naegele's rule uses EDD = LMP + 280 days.
Conception-based dating uses conception date + 266 days.
Ultrasound dating subtracts the entered gestational age from the scan date.
The progress percentage uses a 280-day gestational timeline.

What this tool does not decide

This tool does not confirm or diagnose pregnancy, ovulation, or fertility. Consult a GP, midwife, or fertility specialist.
Viability, scan interpretation, prenatal screening, labour timing, or whether dates should be changed in your medical record.

Sources

Naegele's rule, EDD = LMP + 280 days
Standard conception dating: EDD = conception date + 266 days

Last checked: 2026-06-05

Understanding Your Pregnancy Timeline

Pregnancy is dated from the first day of your last menstrual period (LMP), not from conception. This means you're considered "2 weeks pregnant" at the time of conception, a quirk of medical dating that confuses almost everyone at first. A full-term pregnancy is 40 weeks, or 280 days from LMP.

Only about 5% of babies arrive on their exact due date. Most births occur within a 5-week window from 37 to 42 weeks. Anything from 37 weeks onward is considered full-term. Before 37 weeks is preterm, and after 42 weeks is post-term. Your due date is a best estimate, not a deadline.

Trimester Guide: What to Expect

Trimester	Weeks	Baby's Development	Common Symptoms
First	1 to 12	Organ formation, heartbeat by week 6, all major structures by week 12	Nausea, fatigue, breast tenderness, frequent urination
Second	13 to 26	Rapid growth, movement felt (16 to 22 weeks), sex visible on scan	Energy returns, baby bump appears, back pain may start
Third	27 to 40	Brain development, lung maturation, baby gains most weight	Fatigue returns, Braxton Hicks, heartburn, difficulty sleeping

Key milestone: Week 24 is considered the "viability threshold", the point at which a baby has a reasonable chance of survival if born prematurely, though with significant medical intervention. Survival rates improve dramatically with each additional week: 50% at 24 weeks, 80% at 28 weeks, 95%+ at 32 weeks.

Key Prenatal Appointments

Week	Appointment	What Happens
8 to 10	Booking appointment	Medical history, blood tests, dating scan booked
11 to 14	Dating scan + screening	Nuchal translucency measurement, confirms due date
16	Antenatal check	Blood pressure, urine test, blood test results reviewed
18 to 21	Anatomy scan	Detailed organ check, growth measurements, sex can be determined
25 to 28	Glucose test	Screening for gestational diabetes
36	Position check	Baby's position assessed, birth plan discussed

What to Pack in Your Hospital Bag

For You (Labour)

Birth plan copies, comfortable nightdress or old t-shirt, lip balm, hair ties, snacks (cereal bars, dried fruit), isotonic drinks, phone charger, TENS machine if using one.

For You (After Birth)

Maternity pads (heavy flow), comfortable underwear, nursing bra, going-home outfit (you'll still look 6 months pregnant), toiletries, towel, slippers with grip.

For Baby

Newborn nappies (10+), cotton wool, 2-3 vests, 2-3 sleepsuits, hat, blanket, car seat (hospitals won't let you leave without one), muslin cloths.

Pack your bag by week 36. First babies often come late, but not always, and you don't want to be searching for your phone charger during contractions. Keep the bag by the front door from week 37.

Worked Pregnancy Dating Example

Pregnancy dating starts from gestational age, which is counted from the first day of the last menstrual period. That is why someone can be about 2 weeks pregnant at conception.

Input	Dating rule	Example result
LMP	Add 280 days	Estimated due date
Conception date	Add 266 days	Estimated due date
Ultrasound	Use scan date minus gestational age	LMP-equivalent dating

If your scan date and last-period date do not line up, your midwife or doctor can explain which date is being used in your notes and why.

What Changes the Accuracy of a Due Date?

Irregular Cycles

LMP dating assumes ovulation happens at a predictable point in the cycle. Long, short, or irregular cycles can shift the estimate.

Early Ultrasound

Early scan dating may be preferred when LMP is uncertain or cycles vary. The clinical team decides how to record the date.

IVF Treatment

IVF dating starts from a known transfer date and embryo age, so it can be more precise than spontaneous-conception estimates.

Late Pregnancy Variation

Babies do not arrive exactly on the due date. Progress estimates help with planning but cannot predict labour timing.

Information to Bring to Antenatal Care

First day of your last period, usual cycle length, and whether cycles are regular.
Any positive pregnancy test date, early scan report, IVF transfer date, or conception tracking information.
Current medicines, allergies, previous pregnancies, miscarriage history, and relevant health conditions.
Seek urgent medical advice for heavy bleeding, severe pain, fainting, shoulder-tip pain, or reduced fetal movement later in pregnancy.

Pregnancy Date Review Checklist

Keep a note of the dating basis because due dates can change after clinical review.

Record whether the date came from LMP, conception, IVF, ultrasound, or an existing due date.
Keep scan reports and appointment letters together.
Ask your midwife which EDD is being used in your maternity notes.
Use urgent care routes for concerning symptoms rather than waiting for a routine appointment.

Related Pregnancy Tools

Due Date CalculatorCalculate your estimated due date Conception CalculatorEstimate when you conceived Ovulation CalculatorFind your fertile window BMI CalculatorCheck your pre-pregnancy BMI Water IntakeHydration needs during pregnancy Sleep CalculatorTime your sleep cycles

Part of a workflow

Health & Fitness Workflow

Body baseline → Calories → Nutrition → Training → Progress. 13 tools free.

How to use this tool

Choose due date, last period, ultrasound, conception, or IVF dating

Enter the required date information

Calculate week, trimester, progress, and due date

Common uses

Tracking pregnancy progress by week
Knowing your current trimester
Counting down to your due date
Reviewing upcoming prenatal milestones
Estimating conception date from your due date

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Frequently Asked Questions

How is pregnancy calculated in weeks?

Pregnancy is dated from the first day of your last menstrual period (LMP), not from conception. This means you're considered '2 weeks pregnant' at the time of conception. A full-term pregnancy is 40 weeks or 280 days from LMP.

What is a trimester and when does each one start?

The first trimester covers weeks 1 to 12, when all major organs form. The second trimester spans weeks 13 to 26, when the baby grows rapidly and movement becomes noticeable. The third trimester is weeks 27 to 40, focused on brain development and weight gain.

What milestones should I expect during pregnancy?

Key milestones include: booking appointment (week 8 to 10), dating scan (week 11 to 14), anatomy scan (week 18 to 21), viability threshold (week 24), glucose screening (week 25 to 28), position check (week 36), and full term (week 37+).

Why is pregnancy counted from the last period?

Dating from the last period is standard because most women know when their period started but not when they ovulated. Since ovulation typically occurs around day 14, gestational age runs about 2 weeks ahead of actual fetal age.

How accurate is a pregnancy calculator?

Accuracy depends on the input method. Known due dates from first-trimester ultrasounds are accurate to within 5 to 7 days. LMP-based calculations assume regular cycles, so they can be off by 2 to 3 weeks for women with irregular periods.

What should I do if my dates don't match?

If your LMP-based date and ultrasound date differ by more than 7 days, most clinicians go with the ultrasound date. First-trimester ultrasounds are the gold standard because embryos grow at very predictable rates in the early weeks.

When is the anatomy scan?

The anatomy scan is done between weeks 18 and 21. It checks the baby's organs, growth, placenta position, and amniotic fluid. This is often when the sex can be determined if you want to know.

What is the viability threshold?

Week 24 is considered the viability threshold, the point at which a baby has a reasonable chance of survival if born prematurely, with significant medical intervention. Survival rates improve each week: roughly 50% at 24 weeks, 80% at 28 weeks, 95%+ at 32 weeks.

How does IVF dating differ from natural conception?

IVF dating is the most precise because the fertilisation date is known exactly. For a day-5 blastocyst transfer, the due date is 266 days minus 5 from the transfer date. This removes all guesswork about ovulation timing.

When should I tell my employer I'm pregnant?

Many women wait until after the first trimester (week 12 to 13) when the risk of miscarriage drops significantly. You'll need to formally notify your employer by a certain point to secure maternity leave, check your country's specific rules.

What are Braxton Hicks contractions?

Braxton Hicks are practice contractions that can start from the second trimester. They're irregular, usually painless, and don't dilate the cervix. True labour contractions are regular, progressively stronger, and don't stop when you change position.

How does this calculator handle irregular cycles?

If your cycles are irregular, the LMP method may be less accurate. Use the ultrasound dating option if you have an early scan result, or the conception date option if you tracked ovulation. An early ultrasound is the most reliable method for irregular cycles.

Results are for general informational purposes only and should be checked before use. They are not professional advice. See our Disclaimer and Terms of Service.