# Pregnancy Calculator (Week-by-Week Timeline)

URL: https://speedycalculator.com/calculators/health/pregnancy/
Last updated: 2026-10-30

> The pregnancy calculator builds your pregnancy timeline from your last period, conception date, IVF transfer or ultrasound: due date, current week, trimester dates, the dates of key scans and tests, viability, full term and post-term dates.

## Inputs

- Calculate from
- First day of your last period
- Average cycle length (days)
- Conception date
- Embryo transfer date
- Embryo age at transfer
- Date of ultrasound
- Gestational age at the scan – weeks
- Gestational age at the scan – days
- Due date

## Results

- Due date
- Weeks pregnant today
- …plus days
- Trimester
- Dating / nuchal scan window starts (11 weeks)
- Anatomy scan window starts (18 weeks)
- Viability (24 weeks)
- Glucose test window (24–28 weeks) ends
- Group B strep test (36 weeks)
- Full term (39 weeks)
- Post term (42 weeks)

## Formula

```
Equivalent LMP from your chosen method
Due date = LMP + 280 days
Milestone date = LMP + weeks × 7
```

## Explanation

Knowing when key appointments fall helps you plan: the dating scan at 11–14 weeks, the anatomy scan at 18–22 weeks, the glucose test at 24–28 weeks and the group B strep test at 36–37 weeks.

### How to use the Pregnancy Calculator

- **Calculate from**
- **First day of your last period**
- **Average cycle length**
- **Conception date**
- **Embryo transfer date**
- **Embryo age at transfer**
- **Date of ultrasound**
- **Gestational age at the scan – weeks**
- **Gestational age at the scan – days**
- **Due date**

Results update as you type, and every field accepts the units shown in its menu.

### How it works

Choose what you know and enter the date; the calculator lists the dates for each milestone.

### Inputs explained

FieldWhat to enterCalculate fromChoose one: Last menstrual period, Conception date, IVF transfer date, Ultrasound scan …First day of your last periodA dateAverage cycle lengthIn daysConception dateA dateEmbryo transfer dateA dateEmbryo age at transferChoose one: Day 3 embryo, Day 5 blastocyst, Day 6 blastocystDate of ultrasoundA dateGestational age at the scan – weeksA numberGestational age at the scan – daysA numberDue dateA date

### What each result means

- **Due date** = [Equivalent LMP] + 280
- **Weeks pregnant today** = floor([Days pregnant]÷7)
- **…plus days** = mod([Days pregnant], 7)
- **Dating / nuchal scan window starts (11 weeks)** = [Equivalent LMP] + 77
- **Anatomy scan window starts (18 weeks)** = [Equivalent LMP] + 126
- **Viability (24 weeks)** = [Equivalent LMP] + 168
- **Glucose test window (24–28 weeks) ends** = [Equivalent LMP] + 196
- **Group B strep test (36 weeks)** = [Equivalent LMP] + 252
- **Full term (39 weeks)** = [Equivalent LMP] + 273
- **Post term (42 weeks)** = [Equivalent LMP] + 294

*Health note: this calculator is for education and screening only and is not a diagnosis or treatment advice. Discuss your results with a qualified clinician.*

## Worked example

Inputs — Calculate from: Last menstrual period; First day of your last period: 2026-08-16; Average cycle length: 28 days.

Results — **Due date = Sun, May 23, 2027**; Weeks pregnant today = 10 weeks; …plus days = 6 days; Trimester = First trimester; Dating / nuchal scan window starts (11 weeks) = Sun, November 1, 2026; Anatomy scan window starts (18 weeks) = Sun, December 20, 2026; Viability (24 weeks) = Sun, January 31, 2027; Glucose test window (24–28 weeks) ends = Sun, February 28, 2027; Group B strep test (36 weeks) = Sun, April 25, 2027; Full term (39 weeks) = Sun, May 16, 2027; Post term (42 weeks) = Sun, June 6, 2027.

## Key terms

- **Naegele's rule**: Due date = first day of last period + 280 days (40 weeks).
- **Gestational age**: Pregnancy length counted from the first day of the last period.
- **Trimester**: One of three periods of pregnancy: weeks 1–13, 14–27 and 28 to birth.

## FAQ

**When is the first prenatal appointment?**
Usually around 8–10 weeks.

**What is viability?**
The point, around 24 weeks, when a baby born early has a reasonable chance of survival with intensive care.

**Can I travel in late pregnancy?**
Many airlines restrict flying after 36 weeks (32 for twins); ask your midwife.


## Sources

- [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)
- [NHS – Your pregnancy and baby guide](https://www.nhs.uk/pregnancy/week-by-week/)