Pregnancy Due Date Calculator
Estimate your due date and how many weeks pregnant you are from your last period, conception, an IVF transfer or an ultrasound, with trimester and key dates.
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About this toolWhat is the Pregnancy Due Date Calculator?
Enter the first day of your last menstrual period and this calculator gives your estimated due date, how far along you are in weeks and days, your trimester, and a countdown. If you know something more precise, switch tabs: a conception date, an IVF embryo transfer (day 3, day 5 or day 6 embryo), or the gestational age an ultrasound reported on a given day. All four routes land on the same 40-week clock that midwives and obstetricians use.
Below the headline numbers you get a table of typical milestone dates (first-trimester screening, the anatomy scan, glucose screening, the Tdap vaccine window, the group B strep swab and the term boundaries) and a week-by-week calendar showing which dates fall in each pregnancy week. A due date is an estimate with a spread of a couple of weeks either side, and this page is planning help, not medical advice.
Everything runs in your browser. Nothing is saved and the address bar stays clean; the Copy link button builds a shareable link only when you ask for one.
- Four dating methods: LMP with cycle adjustment, conception, IVF day 3/5/6 and ultrasound
- Weeks + days, trimester, term stage and countdown for any date
- Milestone table from ACOG and CDC timing
- Week-by-week calendar for all 42 weeks
- Calendar maths on local dates, so no off-by-one around midnight or time zones
- Private: no account, nothing stored, link only on request
How to use the Pregnancy Due Date Calculator
- Choose the tab for what you know: Last period, Conception, IVF transfer or Ultrasound.
- Enter the date. For a last period, also check the cycle length; for IVF, pick the embryo age; for a scan, enter the weeks and days the report gave for that day.
- Read the due date, how far along you are today, the trimester and the days left.
- Change "Show progress on" to see how far along you will be on a future date, such as a holiday or a work deadline.
- Scroll to Key dates and the week-by-week calendar, then use Copy summary to paste the main dates into notes or a message.
Worked examples
Last period, 28-day cycle
Input
LMP Thursday 1 January 2026, cycle 28 days
Output
Due Thursday 8 October 2026; conception around 15 January
1 January plus 280 days is 8 October. On 15 March 2026 the calculator shows 10 weeks 3 days, week 11, first trimester.
Long cycle
Input
LMP 1 January 2026, cycle 35 days
Output
Due Thursday 15 October 2026
Seven extra days of cycle push ovulation, and so the due date, seven days later. A 24-day cycle would bring it forward to 4 October.
Frozen embryo transfer
Input
Day-5 blastocyst transferred 20 January 2026
Output
Due 8 October 2026
A day-5 embryo is treated as conceived five days before transfer, so the due date is 261 days after the transfer, matching the LMP example above.
Dating scan
Input
Scan on 12 March 2026 measured 10 weeks 0 days
Output
Due 8 October 2026
The scan date plus 280 minus 70 days. If your LMP had said 20 October, an early scan like this would normally replace it.
Background and insight
Pregnancy is dated from the first day of the last period, not from conception, because that is the date most people know. By convention the due date is 280 days (40 weeks) after that day, which assumes a 28-day cycle with ovulation on day 14. The quick hand method, add seven days, subtract three months and add a year, is credited to the German obstetrician Franz Naegele in the early 1800s. Counting 280 days exactly is more accurate around February: an LMP of 1 January 2024 gives 7 October 2024 by day count, one day earlier than the hand rule, because 2024 had a 29 February.
Cycle length matters because the extra days in a long cycle come before ovulation. With a 35-day cycle ovulation is closer to day 21, so the due date moves seven days later. ACOG Committee Opinion 700 (Methods for Estimating the Due Date, 2017) sets the clinical rules: an early ultrasound takes priority when it disagrees with LMP dating by more than 5 days before 9 weeks or more than 7 days between 9 and 14 weeks, and for IVF the due date comes from the embryo age and transfer date, 261 days after a day-5 transfer and 263 days after a day-3 transfer.
Trimesters here follow ACOG: the first runs to 13 weeks 6 days, the second from 14w0d to 27w6d, the third from 28 weeks. Term labels follow ACOG Committee Opinion 579: early term 37w0d to 38w6d, full term 39w0d to 40w6d, late term 41w0d to 41w6d and post-term from 42 weeks.
Common use cases
Just found out
See roughly how far along you are and when to book a first appointment after a positive test.
IVF pregnancies
Get the due date your clinic will use from the transfer date and embryo age, without counting days by hand.
Checking a scan report
Turn the gestational age on an ultrasound into a due date and compare it with your period-based date.
Planning leave and travel
Find which week of pregnancy a wedding, flight or project deadline falls in.
Partners and family
Share the week-by-week calendar so everyone knows when the third trimester starts.
Tips and limitations
- Use the day bleeding started, not the day it ended or the day you noticed a missed period.
- If your cycles vary a lot, the LMP date is a rough guide. A first-trimester scan is the most accurate way to date a pregnancy.
- Once a scan has set your due date, enter that scan in the Ultrasound tab so this page agrees with your notes.
- Most babies arrive between 37 and 42 weeks. Treat the due date as the middle of a window, not an appointment.
- Milestone timings are typical windows. Your care team may schedule screening differently, especially outside the US.
Frequently asked questions
How is a due date calculated from the last period?
Add 280 days to the first day of your last menstrual period. That equals Naegele's rule (add seven days, subtract three months, add one year) except around a leap day. If your cycle is longer or shorter than 28 days, move the date by the difference: a 32-day cycle adds four days.
How many weeks pregnant am I if conception was two weeks ago?
About four weeks. Pregnancy is counted from the last period, roughly two weeks before conception, so the day of conception is already 2 weeks 0 days. The Conception tab does this offset for you.
How do you calculate an IVF due date for a day-5 transfer?
Add 261 days to the transfer date. For a day-3 embryo add 263 days, and for a day-6 blastocyst 260. These follow ACOG's rule of dating IVF pregnancies from the embryo age and transfer date, and they work the same for fresh and frozen transfers.
Should I trust the ultrasound due date or the period date?
Clinicians usually switch to the scan date when an early ultrasound disagrees with LMP dating by more than 5 days before 9 weeks, or more than 7 days between 9 and 14 weeks. Smaller differences keep the LMP date. Ask your care team which one is in your notes.
What are the exact weeks of each trimester?
Using ACOG's definitions, the first trimester runs to 13 weeks 6 days, the second from 14 weeks 0 days to 27 weeks 6 days, and the third from 28 weeks until birth.
What percentage of babies are born on their due date?
Only about 4 to 5%. Most births happen within a week or two either side, and first babies tend to arrive a little later than later babies. Full term is defined as 39 weeks 0 days to 40 weeks 6 days.
Does this calculator work for twins?
The due date maths is the same, because dating is based on the last period, conception or scan. Twins are usually born earlier, and planned delivery for uncomplicated twin pregnancies is often recommended between about 37 and 38 weeks, so your care team may plan for a date before the one shown.
Is my information saved anywhere?
No. The calculation runs in your browser and the page does not store or send your dates. A link with your inputs is created only if you press Copy link.
Is there an in-depth guide to the Pregnancy Due Date Calculator?
Yes. “How a Due Date Is Calculated, and How Much Weight to Gain” covers the background, how it works, common pitfalls and worked examples. Read the full guide.
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