Pregnancy Due Date Calculator

The Pregnancy Due Date Calculator is a free online tool that estimates your baby’s due date from the first day of your last menstrual period (LMP) using the well-known Naegele rule — and also tells you how many weeks pregnant you are right now and which trimester you are in. That due date becomes the anchor for everything: prenatal appointments, ultrasounds, maternity leave planning, and the nursery timeline. Our free online Pregnancy Due Date Calculator gives you that anchor date in seconds, privately in your browser, with no signup and nothing stored.

How the math works is refreshingly simple: Naegele’s rule adds 280 days (40 weeks) to the first day of the last menstrual period, which for a textbook 28-day cycle is equivalent to adding one year, subtracting three months, and adding seven days. It is the same calculation doctors and midwives have used for centuries — not because it is perfect, but because it is a remarkably good estimate from minimal information. Only about 5% of babies arrive exactly on their due date, but the estimate organizes all of prenatal care around a sensible center point.

A gentle but important note: this calculator is an informational estimate, not medical advice. Real dating also considers cycle length, ovulation timing, and early ultrasound measurements, and your healthcare provider’s dating takes precedence over any online tool. Use our result as a starting point for planning and conversation with your provider — not as a diagnosis. With that understood, it is a genuinely useful first step, sitting among our all free online tools with complete privacy for a deeply personal calculation.

How to Use the Pregnancy Due Date Calculator

One date in, three useful answers out. Here is how to use the calculator and understand what each result means.

1. Open the calculator: The Pregnancy Due Date Calculator is at the top of this page in any modern browser — phone, tablet, or computer. No account, no installation, and nothing you enter is ever stored or transmitted.
2. Find your LMP date: Locate the first day of your last menstrual period. Check a period-tracking app, a calendar, or your memory of it — accuracy here drives everything, since the entire calculation builds on this single date. If you are unsure within a few days, note the uncertainty.
3. Enter the LMP date: Select the date in the tool’s date picker. Take a moment to verify the month and year — an off-by-one-month slip is the most common error and shifts the due date by a full month.
4. Read your estimated due date: The calculator applies Naegele’s rule (LMP + 280 days) and shows your estimated due date. Treat it as the center of a range: most births fall within two weeks on either side, and only about 1 in 20 babies arrives on the exact date.
5. Check weeks pregnant: The tool also computes your current gestational age in weeks and days from the LMP — the same “you are X weeks pregnant” figure your provider uses. This number drives which screenings and appointments are due when.
6. Note your trimester: See which trimester you are in: first (weeks 1–12), second (13–26), or third (27–birth). Each trimester has its characteristic milestones, symptoms, and checkups, so knowing where you stand organizes everything else.
7. Adjust for cycle length if needed: Naegele’s rule assumes a 28-day cycle with ovulation on day 14. If your cycles run consistently longer or shorter, mention it to your provider — they will adjust the dating, since ovulation timing shifts the true gestational age by the difference.
8. Bring the result to your provider: Share the LMP date and the calculator’s estimate at your first prenatal appointment. Your provider will confirm or refine the dating — often with an early ultrasound, which is the most accurate dating method — and that confirmed date becomes your official one.

Enter one date, get your due date, weeks, and trimester. Then let your healthcare provider confirm it — the calculator organizes your planning; your provider manages your care.

Key Features of Our Pregnancy Due Date Calculator

What the calculator provides, built around privacy and simplicity.

• Naegele-rule due date estimation: The standard LMP + 280 days calculation — the same rule behind the wheel calculators in every obstetric office — computed instantly and transparently.
• Current weeks-pregnant count: Gestational age in weeks and days from your LMP, matching the convention your provider uses for scheduling screenings and ultrasounds.
• Trimester identification: Automatic first/second/third trimester placement, so you know which phase of milestones, symptoms, and appointments you are in.
• Completely private: This is deeply personal health information, and it never leaves your device: no accounts, no storage, no analytics on your dates. The calculation happens locally in your browser.
• Free with no signup: No account to create, no email to surrender, no subscription. One date in, answers out, done.
• Works on any device: Use it on your phone in private, on a tablet, or on a desktop — the same instant calculation everywhere, with no app to install.

Pregnancy Due Date Calculator Use Cases

A due date anchors months of planning. The main ways families use it — and our other Calculator tools.

Planning prenatal care

The due date and current week determine the entire prenatal schedule: the 8–12 week first appointment, nuchal translucency screening windows, the 20-week anatomy scan, glucose testing at 24–28 weeks. Knowing your weeks-pregnant count lets you book each appointment in its correct window instead of guessing.

Bring the calculator’s estimate to your first visit so scheduling starts from the right baseline.

Work and leave planning

Maternity/paternity leave, telling your employer, arranging coverage, budgeting for unpaid time — all of it works backward from the due date. An early estimate lets both parents start conversations with employers months ahead, and lets freelancers plan client handoffs around a realistic window rather than a surprise.

Remember the ±2 week reality when committing to exact dates with employers.

Preparing the home and family

Nursery setup, baby gear purchases, childcare waitlists (which can be months long), pet preparations, freezer meals — the due date turns an overwhelming list into a phased timeline. The trimester breakdown helps pace it: research in the second trimester, setup in the third.

Many families work backward from “38 weeks” for must-be-done items, since early arrivals are common.

Tracking milestones week by week

Pregnancy guides, apps, and books are all organized by gestational week — “week 12: first trimester ends,” “week 20: halfway there.” The calculator’s weeks-pregnant figure is the key that unlocks all of them, letting you follow your baby’s development and your body’s changes in sync with every resource you read.

Pair with a reputable week-by-week guide from your provider’s recommended sources.

Background reading: learn more about the concepts behind this tool in the Wikipedia article on Naegele’s rule.

Why Use This Free Online Tool?

You could do this math on a calendar — add 280 days to a date by hand — but date arithmetic across month boundaries is exactly the kind of thing humans botch, and this particular date matters. Our calculator applies Naegele’s rule instantly and also gives you the weeks-pregnant count and trimester that make the date useful, all with absolute privacy: no account, no stored dates, no data trail for something this personal. Free, instant, private — the right way to get the first answer to pregnancy’s biggest question.

Every calculation happens entirely in your own browser. Our Pregnancy Due Date Calculator runs 100% client-side with JavaScript, which means nothing you type, upload, or generate is ever sent to our servers. There is no upload queue, no file-retention policy to read, and no third party ever sees your data — because it never leaves your device. For sensitive documents, personal figures, or private inputs, that architecture is the strongest privacy guarantee a web tool can offer: your information cannot be leaked, sold, or requested from us, because we never had it in the first place.

There is also nothing to install and no account to create. The Pregnancy Due Date Calculator loads instantly on phones, tablets, and desktop computers, works in any modern browser, and is completely free — no trials, no feature gates, and no watermarks. If it saves you time today, you will probably enjoy the rest of the library too: take a look at our full collection of all free online tools to see what else you can do right in your browser.

Tips for Best Results

Get the most accurate estimate and use it wisely. Seven tips.

• Nail down the LMP date: Everything flows from the first day of your last period — not the last day, not ovulation day. Check your tracking app rather than guessing; a few days’ error shifts the whole estimate.
• Know your cycle length: Naegele’s rule assumes 28-day cycles. If yours are consistently 35 days, true ovulation came a week “later” — tell your provider, who will adjust the dating accordingly.
• Treat the date as a range: Think “due month” more than “due date”: only ~5% of babies arrive on the estimated day. Plan around a two-weeks-either-side window to avoid disappointment and logistical tangles.
• Let ultrasound refine it: A first-trimester ultrasound dates pregnancy more accurately than LMP math. The calculator gives you the working estimate; the ultrasound gives you the confirmed one.
• Track weeks, not just the date: Gestational age in weeks is what providers, books, and apps all use. Check your current week regularly — it is the more actionable number day to day.
• This is not medical advice: The calculator is an informational estimate. Any concerns — bleeding, pain, uncertainty about dates, irregular cycles — belong with your healthcare provider promptly, not with a web tool.
• Keep the result private by default: Your dates never leave your device with this tool, but screenshots and shared links can. Share your news on your terms and timeline.

Pregnancy Due Date Calculator FAQs

Common questions about due-date calculation.

How is the due date calculated?

Using Naegele’s rule: 280 days (40 weeks) are added to the first day of your last menstrual period. For a 28-day cycle this equals adding one year, subtracting three months, and adding seven days to the LMP.

How accurate is the estimated due date?

It is an estimate with real variance: only about 5% of babies are born on the exact date, with most arriving within two weeks on either side. First-trimester ultrasound dating is more precise — your provider’s confirmed date takes precedence.

What if I do not know my LMP?

The calculator needs the LMP to work. If your periods are irregular or the date is unknown, an early ultrasound is the reliable dating method — discuss it with your healthcare provider as soon as possible.

What if my cycles are not 28 days?

The rule assumes 28-day cycles with day-14 ovulation. Longer or shorter consistent cycles shift true gestational age; your provider adjusts for this. Mention your typical cycle length at your first appointment.

Is this medical advice?

No. This is an informational estimate for planning purposes. It does not diagnose, predict outcomes, or replace professional prenatal care — always follow your healthcare provider’s guidance.

Is my information private?

Completely. The calculation runs locally in your browser; your LMP date is never transmitted, stored, or logged anywhere. No account exists to tie it to you.

Is the calculator free?

Yes — free, no signup, unlimited use. Recalculate anytime as dates get refined by your provider.

When should I see a doctor?

As soon as you suspect pregnancy — ideally for a first prenatal visit around 8–12 weeks by LMP. Early care and confirmed dating lead to the best outcomes; the calculator is a starting point, not a substitute.

A due date is more than a date — it is the organizing principle for months of appointments, planning, and anticipation. Our Pregnancy Due Date Calculator gives you that anchor in seconds using the classic Naegele rule, plus your current week and trimester, with total privacy and zero cost. Use it to start planning today, and let your healthcare provider confirm the dating that guides your care.

Ready when you are: scroll back up and try the free Pregnancy Due Date Calculator right now — no download, no signup, no cost. And when you are done, explore the rest of our library: all free online tools, our full set of Calculator tools, or jump straight to Scientific Calculator, BMI Calculator, Age Calculator for your next task.