How Many Weeks Pregnant Am I?
HealthEnter the first day of your last menstrual period and your usual cycle length, or the due date your provider gave you. You get how far along you are in weeks and days, the current week of pregnancy and your estimated due date.
Step by step
day 84 = 12+0
- Days from your last period (July 14, 2026) to October 6, 2026, adjusted for the cycle length (28 - 28 days): 84 days.
- Split into completed weeks and days: 12+0, which is week 13 of pregnancy.
- Estimated due date: April 20, 2027.
Once every entry is valid, you’ll see each step of the calculation here.
Formula
- LMP
- first day of the last menstrual period
- cycle length
- average days from one period to the next
- due date
- estimated date of delivery, LMP + 280 days for a 28-day cycle
- ⌊ ⌋
- rounded down to a whole number
How it works
Pregnancy is dated from the first day of your last menstrual period (LMP), about two weeks before conception in a 28-day cycle. This is called gestational age, and it is how doctors and midwives in the US count. A full-term pregnancy lasts about 40 weeks (280 days) from the LMP, so the estimated due date is the LMP plus 280 days. The calculator counts the days from your LMP to the date you check and splits them into completed weeks and days.
The result is written as weeks + days: 13+1 means 13 completed weeks and 1 day, which is the 14th week of pregnancy. If your cycle is longer or shorter than 28 days, ovulation likely came later or earlier, so the calculator shifts the dates by the difference. If you already have a due date from your provider, choose “Due date” and the count starts 280 days before it.
The first trimester runs through 13+6 (13 completed weeks and 6 days), the second from 14+0 to 27+6 and the third from 28+0 to birth. In the week numbering above, that is weeks 1 to 14, 15 to 28 and 29 onward. The American College of Obstetricians and Gynecologists (ACOG) recommends setting the due date by the LMP and checking it with an ultrasound in the first trimester, which is the most accurate way to date a pregnancy. This calculator gives an estimate and does not replace prenatal care. To find your fertile days, see the ovulation calculator.
The formula
For a 28-day cycle the correction is 0. With a 32-day cycle it is 4 days, so the pregnancy counts 4 days less and the due date moves 4 days later. This is the common adjustment of Naegele’s rule; your provider may date the pregnancy differently after an ultrasound.
The current week is the completed weeks plus 1: at 13+1 you are in week 14. Only about 1 in 20 babies arrives on the due date itself; most come within two weeks before or after it.
Example
Your last period started on June 1, 2026. How far along are you on September 1, 2026?
- Days between the two dates: 92 days.
- 92 days are 13 completed weeks and 1 day: you are 13+1, in week 14 of pregnancy, still in the first trimester, which lasts through 13+6.
- The estimated due date is 280 days after the LMP: March 8, 2027, 188 days away.
On September 1, 2026 you are 13+1 pregnant (weeks + days), which is week 14 of pregnancy. Estimated due date: March 8, 2027, 188 days from now.
Load this example into the calculatorFrequently asked questions
How do I calculate how many weeks pregnant I am?
Count the days from the first day of your last period to today and divide by 7. The whole number is the completed weeks and the remainder the extra days. 75 days are 10 weeks and 5 days, written 10+5, which is the 11th week.
How many months pregnant is 12 weeks?
About 3 months, near the end of the first trimester, which runs through 13+6. Pregnancy months are not exact: 40 weeks are often split into 9 calendar months or 10 four-week months. Doctors count in weeks because they are precise.
Why does pregnancy start before conception?
The date of conception is rarely known, but most people know when their last period started. Counting from the LMP adds about two weeks before ovulation, so at conception you are already counted as 2 weeks pregnant.
What if my periods are irregular?
Then the LMP date is less reliable, and an early ultrasound gives a better estimate. Enter the due date from your provider and choose “Due date” to count from it.
Can the due date change?
Yes. ACOG recommends adjusting it when the first-trimester ultrasound differs from the LMP date by more than a set number of days. Once the due date is set by your provider, it usually stays the same for the rest of the pregnancy.
- Methods for Estimating the Due Date (Committee Opinion No. 700) (American College of Obstetricians and Gynecologists)
- Gestational age (MedlinePlus, National Library of Medicine)
- Naegele’s rule (Wikipedia)