What is Pregnancy Week Calculator?

Pregnancy Week Calculator tracks your progress through all 40 weeks. Enter your last period, due date, conception date, ultrasound results, or IVF transfer date to see your current week, baby size comparisons, and developmental milestones.

Pick the input that matches what you know: first day of your last menstrual period, expected due date, conception date, an ultrasound scan with the gestational age it reported, or an IVF embryo transfer date. The tracker pinpoints your current pregnancy week from 1 through 40 and shows the baby's approximate length and weight, a familiar fruit or food for size comparison, key developmental milestones, the body changes you can expect, and a timeline of standard prenatal appointments aligned to your dates.

How to use

1. Step 1 — Pick the mode that matches what you know: last period, due date, conception, ultrasound scan, or IVF transfer.
2. Step 2 — See your current week number with a visual progress bar through all 40 weeks.
3. Step 3 — Read week-specific details about baby development and what to expect.

When to use

• Confirming which week you're in before a midwife or obstetrician appointment.
• Sharing weekly belly photos with family and wanting accurate week labels.
• Reading week-specific advice in pregnancy books without re-counting yourself.

Result

At 20 weeks, the tool shows you're halfway there. Baby is the size of a banana, weighs about 300g, and you may start feeling kicks this week.

FAQ

How does the calculator decide which week I'm in?

It depends on the mode you pick. From your last menstrual period it counts the days since that date and divides by seven. From a due date it works backwards from 40 weeks. From a conception date it adds 14 days to estimate the LMP. From an ultrasound it back-calculates using the gestational age the scan reported. From an IVF transfer it offsets by the embryo age. All follow standard obstetric dating.

Why is the LMP used to count pregnancy if conception happens later?

Most people remember the LMP date reliably, but ovulation and conception dates are rarely known precisely. Obstetricians count from LMP for consistency, even though actual fertilisation usually occurs around week two.

Are the baby size comparisons accurate?

They reflect averages from prenatal reference charts. Real babies vary, especially after week 20 when growth diverges based on genetics and the parent's metabolism. Use the fruit comparisons as a rough mental picture, not a precise measure.

I have irregular cycles. Will the week count be wrong?

Possibly, when dating from LMP alone. Default LMP math assumes a 28-day cycle with ovulation on day 14. If your cycles are reliably longer or shorter, drag the cycle length slider to match — it shifts the conception and due date estimates accordingly. The most accurate option is to switch to the ultrasound mode and enter the gestational age your dating scan reported.

Should I trust this over my doctor's dating?

No. This is a quick reference between visits. If your provider has set a date based on an ultrasound, use that date. Their dating accounts for measurements this tool cannot see.

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