🤰Pregnancy Due Date Calculator
Estimate your due date from your last period, conception date, or an ultrasound — with your current gestational age, trimester, and a normal due window.
Dating method
Default is 28. Adjust if your cycle is consistently longer or shorter — this shifts the estimated ovulation day.
This tool provides an estimated due date only — only about 5% of babies arrive on the exact EDD, and a normal arrival window spans weeks 37–42. A first-trimester ultrasound is generally more accurate than period-based dating and takes precedence when the two differ by more than about a week (per ACOG guidelines). This estimate is not medical advice. Please begin prenatal care early and confirm your dating with your doctor or midwife — they can give you the most accurate information and personalised care throughout your pregnancy.
Free Due Date Calculator Online
Expecting? Our free Due Date Calculator estimates when your baby might arrive the moment you enter a date. As a simple due date calculator, it uses the first day of your last menstrual period — the standard Naegele's rule — to estimate your due date, and you can fine-tune it with your cycle length or switch to a conception or ultrasound date for a closer fit.
Beyond the date, it shows how far along you are right now in weeks and days, which trimester you're in, and a normal "due window" around your estimated date — because only about 1 in 20 babies actually arrives on the exact day. It's a friendly way to follow your pregnancy timeline and plan ahead.
Simply enter your date to see your estimate instantly. No sign-up, no downloads, no limits. Your due date is an estimate — an early ultrasound and your doctor or midwife will give you the most accurate dating and care. Learn more in the FAQ or About pages.
About the Pregnancy Due Date Calculator
What it does
The Pregnancy Due Date Calculator estimates when your baby is likely to arrive based on one of three clinical dating methods. Enter the first day of your last menstrual period and the tool applies Naegele's rule (LMP + 280 days) to produce an estimated due date (EDD). You can also adjust for a non-28-day cycle, switch to a conception or ovulation date, or enter your ultrasound scan date with the gestational age your sonographer measured — whichever gives the best-known starting point.
Beyond the date itself, the tool shows how far along you are right now in weeks and days, which trimester you're in, and a normal due window (37–42 weeks) to make clear that the EDD is an estimate, not a deadline. Everything runs in your browser — no data is stored or sent anywhere.
Key features
Three dating methods
Last menstrual period (with optional cycle-length adjustment), conception or ovulation date, and ultrasound dating using the gestational age at scan. Choose the method that matches what you know.
Estimated due date (EDD)
The EDD is displayed prominently, along with a days-to-go countdown and a plain note about how far away it is — or how many days past the EDD if you are in the late stages.
Current gestational age
Shows your current gestational age in weeks and days, calculated from the effective LMP date to today, updating automatically on each use.
Trimester indicator
First trimester covers weeks 1–13, second trimester weeks 14–27, and third trimester week 28 onward. A colour-coded badge makes it easy to see at a glance.
Normal due window
Shows the 37–42 week date range around your EDD — the normal range of term delivery — so the EDD is framed as the midpoint of a window, not a fixed deadline.
Pregnancy progress timeline
A visual progress bar spanning weeks 0–40 shows where you are in the pregnancy at a glance. It adapts to your current gestational age each time you open the tool.
The dating methods
Last menstrual period (Naegele's rule)
EDD = LMP + 280 days. The most common clinical method, assuming a 28-day cycle with ovulation at day 14. For other cycle lengths the tool adds (cycle length − 28) days to adjust the ovulation assumption. Accurate when the LMP date is reliably known.
Conception / ovulation date
EDD = conception date + 266 days (38 weeks). Useful when the date of conception or ovulation is known from tracking, assisted reproduction, or a positive ovulation test. Equivalent to LMP dating but anchored to fertilisation rather than the last period.
Ultrasound dating
The EDD is back-calculated from the scan date and the gestational age measured by the sonographer. A first-trimester scan (before 13–14 weeks) is the most accurate method clinically, and per ACOG guidelines takes precedence over LMP dating when the two differ by more than about 7 days.
Cycle-length adjustment
When using the LMP method, entering a cycle length other than 28 days shifts the EDD proportionally. This reflects that ovulation — and therefore fertilisation — typically occurs around day 14 of the cycle, so a longer cycle delays it and a shorter cycle advances it.
Why the EDD is an estimate, not a deadline
Ovulation varies
The LMP method assumes ovulation on day 14, but actual ovulation can shift by several days in either direction, even in regular cycles. This alone can move the true due date by a week or more.
Implantation timing differs
After fertilisation, implantation typically occurs 6–10 days later, but the range varies between individuals, adding further uncertainty to the calculated EDD.
Fetal growth is individual
Ultrasound-based gestational age estimates have a margin of roughly ±1–2 weeks in the first trimester and wider later on, because fetal size is naturally variable between pregnancies.
Normal range is wide
Births between 37 and 42 weeks are considered normal term deliveries. Planning around the EDD is useful; treating it as a firm date is not — and clinicians have known this for decades.
Frequently Asked Questions
How does the due date calculator work?
By default it adds 280 days (40 weeks) to the first day of your last menstrual period — the standard Naegele's rule used clinically worldwide. You can also use a conception or ovulation date (adds 266 days) or an ultrasound date with the gestational age your sonographer measured, which back-calculates the same EDD.
How accurate is the estimated due date?
It is an estimate. Only about 5% of babies arrive on the exact EDD, and a normal arrival window spans weeks 37–42 of pregnancy. Individual variation in ovulation timing, implantation, and fetal growth means no formula can pinpoint a single correct date. A first-trimester ultrasound typically narrows the window more than a period-based calculation alone.
Is this calculator free?
Completely free. No sign-up, no downloads, and no limits — just enter a date and get your result instantly.
What if my cycle isn't 28 days?
You can enter your cycle length in the LMP method and the tool shifts the EDD by the difference from 28 days. A 30-day cycle, for example, moves the EDD two days later; a 25-day cycle moves it three days earlier. This adjustment reflects that longer or shorter cycles shift ovulation relative to the period start date.
Can I use my conception or ultrasound date instead of my LMP?
Yes. Select the "Conception Date" method to add 266 days from the date of conception or ovulation. Select "Ultrasound" to enter the scan date and the gestational age your sonographer measured — the tool back-calculates the EDD from those two pieces of information.
Which is more accurate — last period or ultrasound?
A first-trimester ultrasound (before about 13–14 weeks) is generally more accurate than period-based dating, because it directly measures fetal size rather than assuming ovulation timing. Clinically, when an ultrasound EDD and an LMP-based EDD differ by more than about 7 days, the ultrasound date takes precedence (per ACOG guidelines).
How many weeks pregnant am I?
The tool shows your current gestational age in weeks and days — calculated from the effective last menstrual period date to today — along with which trimester you are in. Trimester one covers weeks 1–13, trimester two covers weeks 14–27, and trimester three covers week 28 onward.
Is my data stored anywhere?
No. All date calculations happen entirely in your browser. Your dates are never stored or sent to a server, so your information stays completely private.
Does it work on mobile?
Yes. The tool is fully responsive — inputs and results stack vertically on small screens so everything remains readable and tap-friendly without horizontal scrolling.
Does this replace seeing a doctor?
No. The calculator provides a general planning estimate, not medical advice. Please begin prenatal care early — your doctor or midwife will confirm your dating (usually with a first-trimester ultrasound) and guide your care throughout the pregnancy.