Pregnancy Week Calculator
Find out exactly how many weeks and days pregnant you are, your current trimester, baby’s development stage and remaining time until your due date.
How your weeks are counted
Gestational age is measured from the first day of your last menstrual period (LMP), not from
conception, so it includes roughly two weeks before you were actually pregnant. The calculator counts the days
since your LMP and adjusts for your cycle:
Weeks pregnant = (days since LMP − (cycle length − 28)) ÷ 7
The adjustment keeps the week count consistent with your due date: the standard 40-week clock assumes ovulation on
day 14 of a 28-day cycle, but with a 32-day cycle ovulation is around day 18, so the pregnancy is actually 4 days
"younger" than the raw day count suggests. The due date is the same cycle-adjusted estimate our
Due Date Calculator produces: LMP + 280 + (cycle − 28) days.
Worked example
LMP on 10 April 2026, 28-day cycle, checked on 19 July 2026: 100 days have
passed, which is 14 weeks, 2 days — early in the second trimester, about 36% of the way to the
due date of 15 January 2027, with 180 days to go. At 14 weeks the baby is roughly lime-to-avocado sized.
Trimesters at a glance
| Trimester | Weeks | Highlights |
|---|
| 1st | 0 – 13 | Organs form; morning sickness most common |
| 2nd | 14 – 27 | Anatomy scan; movement usually felt from 18–22 weeks |
| 3rd | 28 – birth | Rapid weight gain; full term from 39 weeks |
The fruit comparison is a fun approximation of average fetal length and weight for the nearest listed week — every
baby grows at its own pace, and only ultrasound measurements track growth accurately.
Frequently asked questions
How many weeks is a full pregnancy?
Pregnancy is counted as 40 weeks (280 days) from the first day of the last menstrual period. "Full term" is 39 weeks 0 days to 40 weeks 6 days; 37–38 weeks is early term, and after 42 weeks is post-term.
Why is pregnancy counted from my last period and not conception?
The last period gives a known, recorded date, while conception usually can’t be pinned down exactly. Counting from the LMP adds roughly two weeks before conception — which is why you are "4 weeks pregnant" only about two weeks after conceiving.
How does cycle length affect my weeks?
The 40-week count assumes ovulation on day 14 of a 28-day cycle. If your cycle is longer, ovulation happens later, so the calculator subtracts one day for every day your cycle exceeds 28 days (and adds days for shorter cycles) so the week count lines up with your adjusted due date.
When do the trimesters start and end?
Using the common convention: 1st trimester up to the end of week 13, 2nd trimester from week 14 to the end of week 27, and 3rd trimester from week 28 to birth.
My ultrasound says a different number of weeks — which is right?
Trust the ultrasound. A first-trimester dating scan is accurate to within about 5–7 days and providers will re-date the pregnancy from it. The LMP method is an estimate that assumes you remember the date correctly and ovulated as predicted.
This tool provides general health information, not medical advice. Consult a healthcare professional before making decisions based on it. Dates are estimates — only an ultrasound can date a pregnancy accurately; always confirm with your healthcare provider.