# How Far Along Am I? Pregnancy Week Calculator

> Pregnancy is counted in weeks from the first day of your last period, and your due date is 40 weeks (280 days) from then. Enter your due date, or your last period, conception date, IVF transfer or scan, to see exactly how many weeks and days pregnant you are today.

- Interactive calculator: https://www.leoella.com/tools/pregnancy-week-calculator
- Plain-text version: https://www.leoella.com/tools/pregnancy-week-calculator.md
- Category: Pregnancy
- Publisher: Leo&Ella (https://www.leoella.com)
- Last reviewed: October 19, 2026

## How it works

The calculator finds day 0 of the pregnancy from what you enter (your due date minus 280 days, your last period, conception date, IVF transfer or a scan) and counts the calendar days from then to today. That count gives the weeks and days pregnant, the week in progress, the trimester and the month of pregnancy, with the 40 weeks grouped into nine months (weeks 1 to 4, weeks 5 to 8, weeks 9 to 13 and so on), plus calendar months to one decimal. Upcoming ACOG trimester and term dates are counted from the same day 0.

## Key facts

- By ACOG's convention, a pregnancy is counted from the first day of the last menstrual period, and the due date is 280 days (40 weeks) after it. [1]
- Because ACOG's dating assumes ovulation on day 14 of a 28-day cycle, a pregnancy is already about 2 weeks along at conception. [1]
- ACOG counts the first trimester as up to and including 13 weeks 6 days of pregnancy. [1]
- ACOG calls a first-trimester ultrasound the most accurate way to establish or confirm how far along a pregnancy is. [1]
- ACOG defines early term as 37 weeks to 38 weeks 6 days, full term as 39 weeks to 40 weeks 6 days, late term as 41 weeks to 41 weeks 6 days, and post-term as 42 weeks or later. [2]
- In a study that pinpointed ovulation, only 4% of women gave birth at exactly 280 days and 70% within 10 days of their estimated due date (ESHRE, 2013). [3]

## Reference data

### How far along you are from your due date

Your due date is day 280: subtract the days still to go from 280.

| Days until due date | How far along | Week in progress | Month of pregnancy | Calendar months |
| --- | --- | --- | --- | --- |
| 210 | 10 weeks | Week 11 | Month 3 | 2.3 |
| 140 | 20 weeks | Week 21 | Month 5 | 4.6 |
| 100 | 25 weeks, 5 days | Week 26 | Month 6 | 5.9 |
| 60 | 31 weeks, 3 days | Week 32 | Month 8 | 7.2 |
| 11 | 38 weeks, 3 days | Week 39 | Month 9 | 8.8 |

### Pregnancy weeks to months

| Month of pregnancy | Weeks | Trimester |
| --- | --- | --- |
| Month 1 | Weeks 1 to 4 | First |
| Month 2 | Weeks 5 to 8 | First |
| Month 3 | Weeks 9 to 13 | First |
| Month 4 | Weeks 14 to 17 | First and second |
| Month 5 | Weeks 18 to 22 | Second |
| Month 6 | Weeks 23 to 27 | Second |
| Month 7 | Weeks 28 to 31 | Second and third |
| Month 8 | Weeks 32 to 35 | Third |
| Month 9 | Weeks 36 to 40 | Third |

### Trimesters and term (ACOG)

| Stage | Starts at |
| --- | --- |
| Trimester 1 starts | 0 weeks |
| Trimester 2 starts | 14 weeks |
| Trimester 3 starts | 28 weeks |
| Early term starts | 37 weeks |
| Full term starts | 39 weeks |
| Late term starts | 41 weeks |
| Post-term starts | 42 weeks |

## Frequently asked questions

### How do I know how far along I am from my due date?

A pregnancy is counted as 280 days (40 weeks) long, ending on the due date. Count the days left until your due date and subtract them from 280: the result is how many days pregnant you are. If your due date is 100 days away, you're 180 days, or 25 weeks 5 days, pregnant.

### How many weeks pregnant am I at conception?

About 2 weeks. Pregnancy weeks are counted from the first day of your last period, and in a 28-day cycle ovulation and conception happen around day 14. So at conception you're already about 2 weeks pregnant, and a missed period comes at about 4 weeks.

### How many months pregnant is 38 weeks 3 days?

It's month 9 of pregnancy, which most guides count as weeks 36 to 40. In calendar months it's about 8.8 months since the first day of your last period. The two don't match because 40 weeks is a little over 9 calendar months.

### When does the second trimester start?

At 14 weeks 0 days. ACOG counts the first trimester through 13 weeks 6 days, the second from 14 weeks through 27 weeks 6 days, and the third from 28 weeks until birth.

### What's the difference between "13 weeks pregnant" and "week 13"?

"13 weeks pregnant" means 13 full weeks have passed. "Week 13" is the week you're in: at 12 weeks 3 days you've finished 12 weeks and are in week 13. This calculator shows both.

### Why does my ultrasound date differ from my period date?

A first-trimester ultrasound (up to 13 weeks 6 days) measures the baby directly and is the most accurate way to date a pregnancy, especially with irregular cycles. If it gives a different due date, your provider will usually go by the scan. Enter that due date here.

## Sources

1. [ACOG Committee Opinion 700: Methods for Estimating the Due Date](https://www.acog.org/clinical/clinical-guidance/committee-opinion/articles/2017/05/methods-for-estimating-the-due-date)
2. [ACOG Committee Opinion 579: Definition of Term Pregnancy](https://www.acog.org/clinical/clinical-guidance/committee-opinion/articles/2013/11/definition-of-term-pregnancy)
3. [ESHRE: Length of pregnancy can vary naturally by as much as five weeks (2013)](https://www.eshre.eu/Press-Room/Press-releases-2013/Length-of-pregnancy-can-vary-naturally-by-as-much-as-five-weeks)

## About this page

This is general information for parents, not medical advice; a doctor, midwife or pediatrician who knows the family should guide individual decisions. The calculator runs in the visitor's browser and stores nothing they enter. When quoting this page, cite "How Far Along Am I? Pregnancy Week Calculator, Leo&Ella" and link https://www.leoella.com/tools/pregnancy-week-calculator.