Pregnancy Due Date Calculator: Find Your Exact Due Date

When you’re expecting, “when is my due date” is usually the very first question, and it’s rarely a single simple answer — it depends on how you’re dating the pregnancy in the first place. Our free pregnancy due date calculator gives you a precise estimate using whichever dating method actually matches your situation: last menstrual period, a known conception date, or an IVF embryo transfer date, with an optional twins adjustment layered on top of any of the three. This page explains exactly how each method is calculated, why the numbers sometimes look different from a friend’s, and how to read your results with confidence.

If you want the general week-by-week tracker with a full pregnancy timeline, our main pregnancy calculator covers that ground too. This page is more focused: it’s built specifically around getting your due date right, comparing methods side by side, and handling the situations — twins, IVF, irregular cycles — that a basic due-date estimate often glosses over.

How this pregnancy due date calculator works

Under the hood, this pregnancy due date calculator runs the same date arithmetic a provider would do by hand, just faster and with the reasoning shown alongside the result. You choose the dating method that actually matches your situation, the pregnancy due date calculator applies the matching formula behind that method, and it returns not just a single date but a plain-language explanation of how that date was reached — so you’re never left staring at a number with no sense of where it came from.

How to use this pregnancy due date calculator, step by step

1. Pick your dating method at the top: Last Menstrual Period, Conception Date, or IVF Embryo Transfer.
2. Enter the one date this pregnancy due date calculator asks for. Only the field that matches your chosen method appears, so you’re never filling in information you don’t have.
3. If you’re using LMP dating and your cycle isn’t a standard 28 days, open the cycle-length field and enter your typical cycle length so the pregnancy due date calculator can adjust for it.
4. If you’re using IVF dating, select Day 3 or Day 5 transfer explicitly — the Calculate button stays disabled until you do, since this choice shifts the result by two days.
5. Turn on the twins toggle if it applies, regardless of which base method you’re using — it works the same way under any of the three.
6. Press Calculate to see your due date, method explainer, and timeline appear instantly below the form.

Because every input on this pregnancy due date calculator updates the result the moment you press Calculate again, it’s easy to compare two scenarios back to back — for example, checking what your due date would look like under a 26-day cycle versus a 30-day cycle, or comparing a Day 3 estimate against a Day 5 estimate if your clinic’s paperwork is ambiguous.

You start by picking a dating method. Only the fields relevant to that method appear, so the form stays short no matter which situation you’re in.

Last Menstrual Period (Naegele’s Rule). This is the default and most commonly used method. You enter the first day of your last period, and this pregnancy due date calculator applies Naegele’s rule — adding 280 days to that date. It’s the same formula that’s been the backbone of obstetric due-date estimation for close to two centuries, and it’s still what most providers use as a starting point today. If your cycles run shorter or longer than the standard 28 days, an optional “adjust for my cycle length” field lets you enter your typical cycle length, and the pregnancy due date calculator shifts the estimate to compensate — a longer cycle generally pushes ovulation (and the due date) later, a shorter cycle pulls it earlier.

Conception date. If you know roughly when conception occurred, you can skip LMP dating entirely and enter that date instead. This pregnancy due date calculator adds 266 days — about 38 weeks — since a full-term pregnancy runs roughly 38 weeks from conception, even though it’s described clinically as 40 weeks from the last period.

IVF embryo transfer. If you conceived through IVF, this pregnancy due date calculator has a dedicated method for it, because LMP-based dating usually isn’t meaningful when conception happened in a lab rather than through a natural cycle. You enter your transfer date and select whether it was a day-3 or day-5 (blastocyst) transfer. A day-3 transfer due date is calculated as 263 days from the transfer date; a day-5 transfer is 261 days from transfer. The two-day gap reflects the two extra days of embryo development a blastocyst has already gone through by the time it’s transferred — both are correct, they’re just measuring from different starting points.

Expecting twins or multiples? A toggle available under any of the three methods above lets you flag a twin or multiple pregnancy. This doesn’t change how your due date itself is calculated — the standard 40-week estimated due date is still shown as the headline figure — but it adds a second, clearly separated card showing a typical delivery-timing estimate around week 36, since twins are, on average, born earlier than singletons. We keep that as an additional data point rather than folding it into the main due date, because “due date” and “typical delivery timing” are genuinely different concepts, and blending them would make the numbers harder to interpret.

What you’ll see in your results

Once you calculate, this pregnancy due date calculator shows:

• Your estimated due date — the standard 40-week EDD, shown as the headline number regardless of whether the twins toggle is on.
• A typical twin delivery-timing estimate, styled as a separate light-blue info panel, only if you’ve turned on the twins toggle — labeled clearly so it reads as an additional note, not a second due date competing with the first.
• A method-explainer line restating which formula was used in plain language — for example, “Calculated using Naegele’s Rule, adjusted for a 30-day cycle” or “Calculated from a Day 5 blastocyst transfer” — so you know exactly what went into your number.
• Current week and day, and trimester, matching the same stats you’d see on our main pregnancy calculator, for continuity if you use both tools.
• A comparison note when your method is IVF, briefly explaining that day-3 transfers are dated two days later than day-5 transfers for an equivalent due date, so a friend’s slightly different-looking “due date math” doesn’t seem like a mistake.
• A simple visual timeline marking your starting date (LMP, conception, or transfer), today, and your due date on one line — plus a twin-timing marker if that toggle is active — so you can see the whole pregnancy at a glance rather than just a single number.

A disclaimer stays visible below your results at all times: due dates are estimates, twin-delivery timing is an average rather than a prediction for any individual pregnancy, and ultrasound dating from a provider takes precedence over any pregnancy due date calculator, including this one.

How accurate is a pregnancy due date calculator, really?

Genuinely useful question, and worth answering honestly rather than glossing over. Research consistently shows that only about 4 to 6 percent of babies are born on their exact calculated due date — most arrive within a week or two of it, in either direction, and that’s considered entirely normal. The World Health Organization defines a full-term pregnancy as anywhere from 37 to 42 weeks, which is a wide window on purpose, not a sign the underlying math is imprecise. That wide window is exactly why any pregnancy due date calculator, this one included, is best read as a planning estimate rather than a fixed deadline.

For LMP-based dating specifically, accuracy hinges on two assumptions: that you remember your last period’s start date correctly, and that your cycle follows something close to a standard 28-day pattern with ovulation around day 14. If your cycles are irregular, if you have PCOS, or if you conceived shortly after stopping hormonal birth control, LMP dating can be off by anywhere from several days to a couple of weeks. Conception-date dating and IVF transfer dating both sidestep that particular source of error, since they don’t depend on assumptions about ovulation timing — which is part of why they’re generally considered more precise when the underlying date is actually known.

If you’ve had a first-trimester ultrasound, that dating typically takes precedence over any pregnancy due date calculator, including ours. Early ultrasound measurements — particularly crown-rump length in the first 12 weeks or so — are considered the most accurate dating method available, often narrowing the estimate to within a few days. If your provider’s ultrasound-based due date differs from what this calculator gives you, go with the ultrasound; this tool is meant to give you a reliable estimate to work with before or between appointments, not to override clinical dating once you have it.

Naegele’s rule: the formula behind LMP dating

Since LMP dating is the default and most-used method here, it’s worth understanding where the underlying formula actually comes from. Naegele’s rule is named after Franz Karl Naegele, a 19th-century German obstetrician, and in its simplest form it works by taking the first day of your last period, subtracting three months, and adding seven days and one year — which lands on the same date as simply adding 280 days. It assumes a 28-day cycle with ovulation on day 14, which is exactly why cycle-length adjustments matter for anyone whose cycle doesn’t match that assumption closely. We’ve written a full breakdown of the rule’s history, the exact math with a worked example, and its known accuracy limitations in our dedicated post on Naegele’s rule, which pairs well with this pregnancy due date calculator if you want to understand the “why” behind the number, not just the number itself.

Before due date calculators moved online, many providers used a simple paper tool called a pregnancy wheel (or OB wheel) to do this same date arithmetic by hand. You line up the first day of your last period on the inner dial, and the outer ring shows the estimated due date along with each week of pregnancy in between — the same Naegele’s Rule logic this calculator uses, just in physical form. Some clinics still keep one on hand because it’s fast to reference during an appointment. See our full pregnancy wheel guide for how to read and use one.

Twin and multiple pregnancy due dates

If the twins toggle applies to you, it’s worth understanding what that adjustment is and isn’t doing. It does not create a separate, twin-specific due date calculation from scratch — it applies a flat informational offset (roughly four weeks earlier) to whichever base method you’ve already used, reflecting the well-documented pattern that twin pregnancies are, on average, delivered closer to week 36 than week 40. This pregnancy due date calculator keeps that twin-timing note visually separate from your main due date for exactly that reason. It’s a typical-timing estimate, not a new due date, and it isn’t modeled differently for triplets or higher-order multiples, since delivery timing varies more at that point and is really a conversation for your care team rather than a calculator. Our twin pregnancy due date calculator post goes deeper into why twins tend to arrive earlier and how to think about that timing alongside your standard due date.

IVF due dates: day 3 vs. day 5 transfers

IVF dating trips people up more than any other method here, mostly because the “263 vs. 261 days” distinction isn’t obvious unless someone explains it. Both numbers are correct — they’re just counting from different starting points, since a day-5 blastocyst has already had two more days of development than a day-3 embryo at the moment of transfer. Getting the transfer-day type wrong when you use a pregnancy due date calculator will shift your estimate by two days, which is a small but real error, so it’s worth double-checking with your clinic’s paperwork if you’re not sure which type you had. That two-day sensitivity is part of why this pregnancy due date calculator forces an explicit day-3-or-day-5 choice instead of quietly assuming one for you. Fresh versus frozen transfers add another layer of nuance we cover, along with a full worked example, in our IVF due date calculator post.

Common mistakes when estimating a due date

A few small input errors account for most of the confusion people run into with any pregnancy due date calculator, ours included. Mixing up the first day of your last period with the day it ended is a common one — the calculator needs the start date, not the end date, since that’s the reference point Naegele’s rule is built around. Entering a cycle length that’s really your average period length rather than the number of days between periods is another frequent mix-up; cycle length means LMP to LMP, typically 20 to 45 days, not the 3 to 7 days your period itself lasts. For IVF dating, assuming Day 5 by default when your clinic actually did a Day 3 transfer will silently shift your due date by two days, which is exactly why the calculator forces an explicit choice instead of quietly defaulting to one. And for twins, remembering that the toggle adds a separate typical-delivery-timing note rather than replacing your standard 40-week due date helps avoid confusion when the two numbers appear side by side.

Frequently asked questions

A note on accuracy

Every date on this page is calculated with real calendar-date arithmetic — including correct handling of leap years — using the same underlying logic as our main pregnancy calculator, so the two tools will always agree with each other for the same inputs. Still, a pregnancy due date calculator produces an estimate for planning purposes, not a medical diagnosis. Always confirm your due date with your healthcare provider, and treat ultrasound-confirmed dating as the more authoritative number once you have it.