Pregnancy Due Date Calculator — When Is the Baby Due?
Due date from your last period, conception date or IVF transfer — plus how far along you are.
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Key dates
Estimate your due date from whichever date you actually know: the first day of your last period, the conception date, or an IVF embryo transfer. You'll also see how far along you are today, which trimester you're in, and a timeline of the key weeks ahead.
The period method adjusts for your cycle length — the standard rule silently assumes a 28-day cycle, and if yours runs longer or shorter, the unadjusted date can be off by a week.
How to use Due Date Calculator
- Pick what you know: last period, conception date, or IVF transfer.
- Enter the date. For the period method, set your average cycle length too.
- Read your due date and progress — weeks and days, trimester, and weeks remaining.
- Check the key-dates table for the milestones your antenatal care will be scheduled around.
How due dates are calculated
Pregnancy is counted from the first day of the last period — gestational age — even though conception happens about two weeks later. Naegele's rule adds 280 days (40 weeks) to that date, assuming a 28-day cycle with ovulation on day 14. If your cycle averages 33 days, ovulation lands about 5 days later, so this calculator shifts your dates accordingly — the adjustment most quick calculators skip.
From a known conception date the maths is 266 days. IVF is the most precise anchor of all: the embryo's age is known to the day, so a day-5 transfer means 261 days from transfer.
How accurate is this?
Honest answer: it's a well-informed estimate. Only about 4% of babies arrive on their due date; two-thirds arrive within a week of it, and almost all within two weeks either side. Clinicians treat "term" as the whole window from 37 to 42 weeks. Your first-trimester ultrasound measures the embryo directly and is more accurate than any calendar method — when the scan date differs from the period-based date by more than a few days, clinics use the scan.
The weeks that matter
- Week 12–13 — end of the first trimester; miscarriage risk drops sharply, which is why many people share the news around now.
- Weeks 18–22 — the anatomy scan.
- Week 28 — third trimester begins; appointments get more frequent.
- Week 37 — "early term": arriving from here is normal.
- Weeks 39–40 — full term and the due date itself.
Not medical advice
This tool does calendar arithmetic well, but it knows nothing about you or your pregnancy. Confirm dates with your midwife or doctor, and raise anything unusual with them rather than a website — any website.
Frequently asked questions
How accurate is a due date?
It's the middle of a window, not a deadline: only ~4% of babies arrive on the day, about two-thirds within a week of it, nearly all within two weeks either side. The first-trimester ultrasound gives the most accurate date of all and overrides calendar methods when they disagree by more than a few days.
Why does my cycle length change the date?
The standard rule assumes ovulation on day 14 of a 28-day cycle. With a 33-day cycle, ovulation — and therefore conception — happens about 5 days later, so every milestone shifts 5 days too. Enter your average cycle length and this calculator makes that adjustment; most quick calculators silently don't.
How many weeks pregnant am I?
Enter your date and the answer appears as weeks + days ("12 weeks and 3 days"), counted the way clinics count — from the last period, not from conception. That's why you're "4 weeks pregnant" around the time a period is first missed.
How is an IVF due date calculated?
Most precisely of all, because the embryo's age is known exactly: 261 days from a day-5 blastocyst transfer, 263 from a day-3 transfer. Cycle length is irrelevant for IVF, which is why it's a separate tab.
When is it safe to announce a pregnancy?
There is no rule — only the pattern that many people wait until the end of the first trimester (week 12–13), when miscarriage risk has fallen sharply and the dating scan has usually confirmed things. The key-dates table shows where that falls for you. Announce when it feels right.
What do "early term" and "full term" mean?
Clinically, 37–38 weeks is early term, 39–40 full term, 41 late term and 42+ post-term. Babies arriving anywhere in that range are arriving on schedule in the medical sense — the single "due date" is just the 40-week midpoint of it.