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Pregnancy Calculator

Find your due date, current week and trimester dates.

Last updated: Free, no sign-up Private — runs in your browser

Quick answer: how to find your due date

Add 280 days (40 weeks) to the first day of your last period. For a period starting 15 January 2026 the due date is Thursday, 22 October 2026 — and on 15 April 2026 you would be 12 weeks 6 days pregnant.

Overview of the Pregnancy Calculator

The Pregnancy Calculator turns one date into a complete picture: your estimated due date, how many weeks and days pregnant you are today, which trimester you are in, and a week-by-week calendar. You can start from your last menstrual period, conception date, an IVF embryo transfer date or an early ultrasound.

Pregnancy is counted from the first day of the last period, which is about two weeks before conception — so at 'week 4' you are only about two weeks past conception. Dates are estimates; your doctor or midwife will confirm them with a scan. For a simpler due date use the Due Date Calculator; track weight with the Pregnancy Weight Gain Calculator.

How We Calculate

The calculator applies the standard published formulas step by step.

  1. For the last period (LMP) method: due date = LMP + 280 days, adjusted by (your cycle length − 28) days.
  2. From conception: due date = conception + 266 days. IVF: embryo transfer date + 263 days (3-day) or + 261 days (5-day).
  3. From an ultrasound: due date = scan date + (280 − gestational age in days).
  4. Gestational age today = (today − estimated LMP) in weeks and days.
  5. Trimesters: first up to 13 weeks 6 days, second 14–27 weeks 6 days, third from 28 weeks.
due date = LMP + 280 days (+ cycle length − 28)   = conception + 266 days
Worked example — pregnancy calculator
ItemValue
Estimated due dateThursday, 22 October 2026
Pregnancy progress12 weeks 6 days (week 13)
Days until the due date190
Estimated first day of last periodThursday, 15 January 2026
Estimated date of conceptionThursday, 29 January 2026
First trimesterThursday, 15 January 2026 – Wednesday, 22 April 2026
Second trimesterThursday, 23 April 2026 – Wednesday, 29 July 2026
Third trimesterThursday, 30 July 2026 – Thursday, 22 October 2026
Full-term window (39–40 weeks 6 days)Thursday, 15 October 2026 – Wednesday, 28 October 2026
Delivery window (37–42 weeks)Thursday, 1 October 2026 – Thursday, 5 November 2026
Key milestones
WeekDate it startsWhat happens
Week 4Thursday, 12 February 2026Missed period — a home pregnancy test can show positive
Week 8Thursday, 12 March 2026Early dating ultrasound is often done around now (6–9 weeks)
Week 12Thursday, 9 April 2026Many people share the news; the first-trimester screening scan is at 11–13 weeks + 6 days
Week 14Thursday, 23 April 2026Second trimester begins
Week 20Thursday, 4 June 2026Anatomy (anomaly) scan, usually between 18 and 22 weeks
Week 24Thursday, 2 July 2026Glucose screening is commonly offered between 24 and 28 weeks
Week 28Thursday, 30 July 2026Third trimester begins
Week 36Thursday, 24 September 2026Baby is usually head-down; weekly checks may start
Week 37Thursday, 1 October 2026Early term begins (full term from 39 weeks)
Week 40Thursday, 22 October 2026Estimated due date
Week 42Thursday, 5 November 2026Post-term — doctors usually plan induction before this
Week-by-week pregnancy calendar
WeekStarts onTrimester
4Thursday, 12 February 2026First
5Thursday, 19 February 2026First
6Thursday, 26 February 2026First
7Thursday, 5 March 2026First
8Thursday, 12 March 2026First
9Thursday, 19 March 2026First
10Thursday, 26 March 2026First
11Thursday, 2 April 2026First
12Thursday, 9 April 2026First
13Thursday, 16 April 2026First
14Thursday, 23 April 2026Second
15Thursday, 30 April 2026Second
16Thursday, 7 May 2026Second
17Thursday, 14 May 2026Second
18Thursday, 21 May 2026Second
19Thursday, 28 May 2026Second
20Thursday, 4 June 2026Second
21Thursday, 11 June 2026Second
22Thursday, 18 June 2026Second
23Thursday, 25 June 2026Second
24Thursday, 2 July 2026Second
25Thursday, 9 July 2026Second
26Thursday, 16 July 2026Second
27Thursday, 23 July 2026Second
28Thursday, 30 July 2026Third
29Thursday, 6 August 2026Third
30Thursday, 13 August 2026Third
31Thursday, 20 August 2026Third
32Thursday, 27 August 2026Third
33Thursday, 3 September 2026Third
34Thursday, 10 September 2026Third
35Thursday, 17 September 2026Third
36Thursday, 24 September 2026Third
37Thursday, 1 October 2026Third
38Thursday, 8 October 2026Third
39Thursday, 15 October 2026Third
40Thursday, 22 October 2026Third
41Thursday, 29 October 2026Third
42Thursday, 5 November 2026Third
Estimated due date
CaseDue date
Last period 15 Dec 2025Monday, 21 September 2026
Last period 15 Jan 2026Thursday, 22 October 2026
Last period 15 Feb 2026Sunday, 22 November 2026
32-day cycleMonday, 26 October 2026
26-day cycleTuesday, 20 October 2026

Pregnancy Calculator — Frequently Asked Questions

How is the due date calculated?

Naegele's rule adds 280 days (40 weeks) to the first day of the last period, adjusted if your cycle is longer or shorter than 28 days.

How many weeks pregnant am I?

Count from the first day of your last period. The calculator shows the weeks and days as of today, or any date you choose.

When does the first trimester end?

At 13 weeks and 6 days. The second trimester runs from week 14 to 27 and the third from week 28 until birth.

How accurate is a due date?

Only about 4–5% of babies are born on their due date; most arrive between 37 and 42 weeks. An early ultrasound gives the best dating.

What if my cycles are irregular?

An ultrasound-based due date is more reliable than an LMP date if your cycles are irregular or you are unsure of your dates.

When is a pregnancy considered full term?

From 39 weeks to 40 weeks and 6 days. 37–38 weeks is early term, and 42 weeks is post-term.

How is the pregnancy calculator calculated?

It uses the published formula: due date = LMP + 280 days (+ cycle length − 28)   = conception + 266 days The full method and a worked example are shown on this page.

Is this medical advice?

No. The calculator gives general estimates for information and education. It cannot diagnose or treat anything, so please speak to a doctor or qualified professional about your own health.

Can I use US or Indian units?

Yes. Choose centimetres or feet and inches for height, and kilograms, pounds or stone for weight; the results are converted for you.

Is my data stored?

No. Everything is calculated in your browser and nothing you enter is uploaded or saved.

More Free Calculators You May Need

Due Date CalculatorEstimate your baby's due date from five different starting points.Pregnancy Weight Gain CalculatorSee the recommended weight gain for your pregnancy.Conception CalculatorEstimate when you are most likely to conceive and your possible due date.Ovulation CalculatorPredict your ovulation day and fertile window for six cycles.Period CalculatorPredict your next periods, ovulation and fertile days.Date CalculatorAdd or subtract days, months and years — or find the gap between two dates.

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