How far along is my pregnancy?
Enter the first day of your last period, your due date, an ultrasound result or the conception date. See how far along you are, your trimester, and the key dates ahead.
- How far along
- 12 weeks
On September 29, 2026 you are 12 weeks pregnant (First trimester). Estimated due date: April 13, 2027.
- Stage
- First trimester
- Estimated due date
- April 13, 2027
- Days until the due date
- 196
- Share of 40 weeks
- 30%
- Pregnancy counted from
- July 7, 2026
- Likely conception date
- July 21, 2026
- Second trimester starts
- October 13, 2026
- Third trimester starts
- January 19, 2027
- Full term from
- April 6, 2027
Answer for the example date Tuesday, September 29, 2026. It changes to today's date when the page loads.
How far along: 12 weeks. On September 29, 2026 you are 12 weeks pregnant (First trimester). Estimated due date: April 13, 2027.
Where are you in the pregnancy?
This calculator gives general information only. It is not medical advice and does not replace a doctor or other health care provider. Talk with a professional about your results. Terms of use
How to calculate
Works out how many weeks and days pregnant you are on a date, the trimester, the due date and milestone dates, from the last period, the due date, an ultrasound or the conception date.
Example with the default inputs (Based on Last period, First day of your last period July 7, 2026, Cycle length (days) 28, Work out on September 29, 2026) on the example date Tuesday, September 29, 2026: On September 29, 2026 you are 12 weeks pregnant (First trimester). Estimated due date: April 13, 2027.
Method: Weeks pregnant = (date − start) ÷ 7, where the start is the first day of the last period + (cycle length − 28) days, the due date − 280 days, the ultrasound date − the gestational age it gave, or the conception date − 14 days.
- A pregnancy is counted from the first day of the last period and lasts 280 days (40 weeks) to the due date (ACOG).
- Ovulation and conception happen 14 days before the next period would start, so a cycle longer or shorter than 28 days moves the dates by the difference.
- Trimesters: first to 13 weeks 6 days, second from 14 weeks 0 days, third from 28 weeks 0 days. Full term starts at 39 weeks 0 days.
- Before the start, or more than 44 weeks after it, how far along is left out and a note says so.
- An estimate, not medical advice: a first-trimester ultrasound is the most accurate way to date a pregnancy.
Worked examples
Each example is checked against the calculator on every build.
- Based on Last period, First day of your last period 2026-06-01, Cycle length (days) 28, Work out on 2026-09-27 gives How far along 16 weeks, 6 days, Stage Second trimester, Your due date 2027-03-08, Days until the due date 162, Share of 40 weeks 42.142857%, Second trimester starts 2026-09-07, Third trimester starts 2026-12-14, Full term from 2027-03-01.Source: ACOG Committee Opinion 700 (LMP + 280 days) and trimester limits; hand calculation in content.mdx
- Based on Due date, Your due date 2026-12-25, Work out on 2026-09-27 gives Pregnancy counted from 2026-03-20, How far along 27 weeks, 2 days, Stage Second trimester, Days until the due date 89.Source: ACOG CO 700 (due date = start + 280 days); hand calculation in content.mdx
- Based on Conception date, Date of conception 2026-02-14, Work out on 2026-09-27 gives How far along 34 weeks, 1 day, Stage Third trimester, Your due date 2026-11-07, Days until the due date 41.Source: ACOG CO 700 (conception about day 14); hand calculation in content.mdx
- Based on Ultrasound, Ultrasound date 2026-07-01, Weeks at the scan 8, And days 2, Work out on 2026-09-27 gives Pregnancy counted from 2026-05-04, How far along 20 weeks, 6 days, Your due date 2027-02-08.Source: ACOG CO 700 (dating by ultrasound); hand calculation in content.mdx
How it works
The calculator finds the start of the pregnancy count (day 0), from what you know:
- Last period: start = first day of the last period + (cycle length − 28) days
- Due date: start = due date − 280 days
- Ultrasound: start = ultrasound date − (weeks × 7 + days) the scan gave
- Conception date: start = conception date − 14 days
The cycle adjustment: dating from the last period assumes ovulation on day 14 of a 28-day cycle (ACOG), and ovulation happens about 14 days before the next period. In a cycle of C days, ovulation is on day C − 14, so the start moves by C − 28 days. Cycle length can be 21 to 45 days.
Then, on the work-out date (today unless you change it under "Use another date"):
- Days pregnant = work-out date − start.
- How far along = whole weeks and days: days ÷ 7, and the remainder.
- Stage (the trimester): "First trimester" under 98 days (to 13 weeks 6 days), "Second trimester" under 196 days (to 27 weeks 6 days), "Third trimester" under 294 days, then "Past 42 weeks (post-term)". Outside the pregnancy it reads "Before the pregnancy count starts: check the dates" or "More than 44 weeks after the pregnancy count starts: check the dates".
- Due date = start + 280 days. Days until the due date = 280 − days, shown up to the due date.
- Share of 40 weeks = days ÷ 280 × 100, at most 100%.
- Dates ahead: likely conception = start + 14 days; second trimester = start + 98 days; third trimester = start + 196 days; full term (ACOG) = start + 273 days (39 weeks 0 days).
If the work-out date is before the start, or more than 308 days (44 weeks) after it, how far along, the days left and the share are left out, and the stage says the date is outside the pregnancy. All dates are calendar dates with no time of day.
The timeline shows the three trimesters with your work-out date marked.
Assumptions
- Cycles are regular. Real cycles vary (Bull and others, 2019), and a first-trimester ultrasound dates a pregnancy best (ACOG).
- This calculator gives an estimate. It is not medical advice. Your obstetric provider sets your dates; talk to them about your pregnancy.
Worked examples by hand
Last period June 1, 2026, 28-day cycle, worked out on September 27, 2026. Start = June 1. Days: June has 30 days, so June 1 to July 1 is 30, to August 1 is 61, to September 1 is 92, and to September 27 is 118. 118 = 16 × 7 + 6, so 16 weeks 6 days, second trimester. Due date = June 1 + 280 days = March 8, 2027, 280 − 118 = 162 days away. Share of 40 weeks: 118 ÷ 280 = 42%. Second trimester started September 7, 2026 (day 98); the third starts December 14, 2026 (day 196); full term from March 1, 2027 (day 273).
Due date December 25, 2026, on September 27, 2026. Start = December 25 − 280 days = March 20, 2026. From March 20 to September 27 is 191 days = 27 weeks 2 days, still the second trimester (the third starts at 196 days). 89 days to go.
Conception February 14, 2026, on September 27, 2026. Start = February 14 − 14 = January 31, 2026. Days = 239 = 34 weeks 1 day, third trimester. Due date = January 31 + 280 = November 7, 2026, 41 days away.
Ultrasound on July 1, 2026 at 8 weeks 2 days, on September 27, 2026. Start = July 1 − 58 days = May 4, 2026. Days = 146 = 20 weeks 6 days. Due date = May 4, 2026 + 280 days = February 8, 2027.
Other questions people ask
How do I work out how many weeks pregnant I am?
Count the days from the first day of your last period to today, then divide by 7. The whole number is the weeks and the remainder is the days. For example, from June 1 to September 27, 2026 is 118 days, which is 16 weeks 6 days.
Why are pregnancy weeks counted from my last period?
The first day of the last period is a date most people know, while the day of conception usually is not. Counting from it adds about 2 weeks before conception, so a pregnancy is 40 weeks (280 days) long on this count.
I know my due date. How far along am I?
Choose "Due date". The calculator counts back 280 days to find the start, then counts forward to today. With a due date of December 25, 2026, on September 27, 2026 you are 27 weeks 2 days pregnant.
When does each trimester start?
The second trimester starts at 14 weeks 0 days and the third at 28 weeks 0 days. The first trimester runs to 13 weeks 6 days. The calculator shows the dates for your pregnancy.
What does full term mean?
ACOG calls a birth from 39 weeks 0 days to 40 weeks 6 days full term. From 37 weeks 0 days to 38 weeks 6 days is early term, 41 weeks is late term, and 42 weeks or more is post-term.
Which date should I use?
Use the due date your provider gave you if you have one, because it may come from an ultrasound. ACOG says a first-trimester ultrasound is the most accurate way to date a pregnancy.