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
| Field | What to enter |
|---|---|
| Calculate from | Choose one: Last menstrual period, Conception date, IVF transfer date, Ultrasound scan … |
| First day of your last period | A date |
| Average cycle length | In days |
| Conception date | A date |
| Embryo transfer date | A date |
| Embryo age at transfer | Choose one: Day 3 embryo, Day 5 blastocyst, Day 6 blastocyst |
| Date of ultrasound | A date |
| Gestational age at the scan – weeks | A number |
| Gestational age at the scan – days | A number |
| Due date | A 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.
Formula
Equivalent LMP from your chosen method
Due date = LMP + 280 days
Milestone date = LMP + weeks × 7
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.
Frequently asked questions
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.