Pregnancy Calculator & Due Date Estimator
Pregnancy Calculator
Due Date & Weekly ProgressInstantly calculate your due date and see how far along you are.
Private by design · calculated on your device🌼 Your pregnancy details
Choose how you’d like to calculate, enter your date, and we’ll map your due date, progress, and milestones.
▶ Advanced · twins or multiples
🗓️ Your pregnancy milestones
Key moments ahead, in plain language, with the dates they fall on for you.
A gentle, honest note
This is an estimate, not a diagnosis. A due date marks 40 weeks, but only about 1 in 20 babies arrive on it — a healthy arrival anywhere from a few weeks before to a little after is completely normal.
Dating methods differ in accuracy. If your cycles are irregular, an early ultrasound is more reliable than an LMP estimate, because it measures the baby directly rather than assuming when you ovulated. If you’re expecting twins or multiples, they often arrive earlier than a 40-week calendar estimate suggests.
I’m Emma Bennett — I write and maintain this tool from the practical, been-there side of tracking and planning. I’m not a medical professional, and the clinical points here (viability, ultrasound accuracy, multiples) reflect published sources rather than personal advice. This tool hasn’t yet been reviewed by a licensed clinician. For personalized dating or any concern, please talk with your midwife or doctor.
Sources: ACOG, NHS, Mayo Clinic, Cleveland Clinic, and womenshealth.gov guidance on pregnancy dating, gestational age, and fetal development.
I did not expect a due date to feel like a moving target. I had used Luna for months to get a sense of my own cycle, so when the day finally came to actually plan around a pregnancy, I assumed one date would just appear and stay put. It did not. My last period gave me one date, an early scan gave me another, and I spent an evening trying to figure out which one to trust.
That is the reason this calculator asks for more than just your last period. A due date is an estimate built from whichever piece of information you actually have, and the method matters. This page walks through every input, what each result means, and which method to lean on if two dates ever disagree.
You can run the calculator first and read along, or read first and try it after. Either way works.
Once you’ve got a due date to look forward to, browsing names can be part of the fun too, the Baby Name Generator covers girl and boy names across five regions, with no sign-up needed.
How to use the pregnancy calculator
The calculator works entirely from dates you already have, whether that is your last period, a known conception date, an IVF transfer date, or a date from an ultrasound. Pick whichever one you actually know. You do not need all five.
- Choose your calculation method. The dropdown at the top sets which fields show up next: last period, conception date, IVF transfer, ultrasound, or a due date you already have from a provider.
- First day of your last period. If you are using the LMP method, this is the anchor date, the same one Luna uses for ovulation. Alongside it, set your average cycle length. The default is 28 days, but if yours runs longer or shorter, adjust the slider, since a longer cycle pushes both ovulation and your due date a little later.
- Conception date. If you know roughly when conception happened, usually from tracking ovulation or a known date of intercourse, this method counts your due date as about 266 days from there, skipping the cycle-length guesswork entirely.
- IVF transfer date. Choose your transfer date and whether it was a Day 3 or Day 5 transfer. The two are dated differently on purpose. A Day 5 embryo is already older at transfer than a Day 3 embryo, so the due date math shifts to account for that.
- Ultrasound date and gestational age at scan. Enter the date of your scan and the gestational age your provider gave you at that visit, in weeks and days. This method tends to be the most reliable one here, especially if your cycles are irregular, since it measures the pregnancy directly instead of estimating backward from a date.
- Known due date. If a provider has already given you a due date, enter it directly and the calculator works backward to show your current week, trimester, and milestone dates.
There is also an advanced toggle for twins or multiples. Switching it on does not change your due date, since that adjustment is a clinical one your provider makes, not a calendar calculation. What it does is add a note reminding you that multiples often arrive earlier than a standard 40-week estimate.
Once your details are in, tap Calculate my due date. Reset clears everything if you want to compare two methods side by side, which is exactly what I did the week I had both a last-period date and a scan date and wanted to see how far apart they landed.
A small habit that helps
If you get an ultrasound, ask your provider for the exact gestational age they measured, in weeks and days, not just the due date they wrote down. That single number is what lets you compare a scan-based estimate against a last-period estimate here, rather than just trusting one number blind.
How to read your results
Once you calculate, the tool shows a progress ring, a set of stat cards, a size comparison, and a milestone timeline. Here is what each piece is telling you.
| What you see | What it means | What you might do with it |
|---|---|---|
| Progress ring | Where you are in the full 40 weeks, color coded by trimester, rose for the first, teal for the second, gold for the third. | A quick visual sense of how far along you are and how much is left. |
| Due date | Your estimated delivery date, based on the method you chose. | The number to plan around, while remembering only about 1 in 20 babies actually arrive on it. |
| Current trimester | Which of the three trimesters you are in right now. | Context for what your body and the pregnancy are generally doing at this stage. |
| Days remaining | A live countdown to your due date, shown as weeks and days or total days, whichever you prefer. | Practical for planning leave, travel, or a hospital bag timeline. |
| Conception date estimate | Roughly when conception happened, worked out from whichever method you used. | Useful context, especially if you are cross-checking against a date you already had in mind. |
| Size comparison | A simple size reference for the current week. | A lighter, easier way to picture where things stand than a number alone. |
| Milestone timeline | Key dates ahead, in plain language, from the end of the first trimester through your due date. | A map of what is coming and roughly when, so nothing feels sudden. |
If you have used Luna before, this will feel familiar. It is the same idea as the cycle ring, just stretched across nine months instead of one cycle.
Which calculation method is most accurate
Not all five methods carry the same level of precision, and it is worth knowing where each one sits before you lean on a date.
Ultrasound dating is generally the most accurate, particularly a scan done in the first trimester. It measures the pregnancy directly rather than estimating backward from a date you may only remember approximately, which matters most if your cycles are irregular or you are not entirely sure of your last period.
Conception and IVF transfer dates are close behind, since both skip the guesswork of estimating ovulation from a calendar. An IVF transfer date is especially precise, because the embryo’s age is known exactly at transfer.
Last period (LMP) dating is the standard default, and the one most calculators, including this one, use first, since it only requires a date most people already know. It assumes a fairly typical cycle, which is why adjusting your cycle length matters, a longer or shorter cycle shifts both ovulation and the due date that follows it. If your period length itself varies, that is a separate factor from cycle length, and it is covered in more depth in if my period lasts 3 days, when do I ovulate.
If two dates disagree, an ultrasound date should generally take priority over an LMP estimate, and your provider’s judgment should take priority over any calculator, including this one.
Pregnancy by trimester
Three trimesters, roughly thirteen weeks each, though the exact split shifts slightly depending on how your due date lands.
| Trimester | Roughly weeks | What is generally happening |
|---|---|---|
| First | 1 to 13 | The earliest structures form. This stretch actually starts counting from your last period, not conception, which is part of why the very first weeks can feel confusing. The two week wait between ovulation and a missed period is technically already inside weeks one and two. |
| Second | 14 to 27 | Often called the more comfortable stretch. Growth becomes more visible and steady. |
| Third | 28 to 40 | The final stretch, building toward your due date. |
For the fuller picture, all three trimesters explained in depth, plus what’s developing at each stage, see Pregnancy Stages and Trimesters Explained.
This page shows where you are today and what is directly ahead in the milestone timeline. If you want the full week-by-week picture, including a size comparison for every single week rather than just your current one, the Pregnancy Week-by-Week Tracker is built for exactly that.
If you are still working out your own timing rather than reading this after the fact, best time to get pregnant covers how to line up your fertile window with when you would actually want to conceive.
Due dates for twins and multiples
If you are expecting more than one, switching on the twins or multiples toggle does not change your due date here, and that is deliberate rather than a missing feature. Adjusting a due date for multiples is a clinical decision your provider makes based on your specific pregnancy, not something a calendar calculation should guess at.
What the toggle does instead is add a plain reminder: twins and other multiples are, on average, born earlier than a single-baby pregnancy, often somewhere in the mid to late third trimester rather than at the standard 40-week mark. The 40-week estimate this tool gives you is still a useful reference point, just one to hold a little more loosely if you are expecting more than one.
If you conceived through IVF
An IVF due date is calculated differently from a natural conception, because the embryo’s age is already known precisely at transfer, there is no need to estimate backward from ovulation the way an LMP method has to.
The distinction that matters is Day 3 versus Day 5. A Day 5 embryo, often called a blastocyst transfer, is two days older at the moment of transfer than a Day 3 embryo. That two-day difference shifts the due date calculation accordingly, which is why the tool asks which type of transfer you had rather than just the date itself.
This method tends to be one of the more precise ones available here, alongside ultrasound dating, since it does not depend on remembering a last period date or assuming a typical cycle length.
Questions people ask me about their due date
How accurate is a due date calculator?
Think of it as a well-informed estimate, not a guarantee. Only about 1 in 20 babies actually arrive on their calculated due date. What it gives you instead is a reliable window, generally a couple of weeks either side, to plan around.
Is this the same method NHS and ACOG use to calculate a due date?
Yes, for the standard case. This calculator uses Naegele’s rule for the last-period method, the same 280-day estimate used by the NHS, ACOG, and most clinical due date calculators.
Where it can differ from a single in-office calculator is in the extra methods it offers, IVF transfer dating and ultrasound-based dating included, since a lot of official calculators only take your last period. I
f your provider has given you a due date from an early ultrasound, that date is generally more accurate than a last-period estimate, and it’s worth using the ultrasound option here or simply trusting your provider’s date over this one.
Can I calculate my due date from my conception date instead of my last period?
Yes. If you know roughly when conception happened, that method skips the cycle-length estimating entirely and counts forward about 266 days, which can be more precise than a last-period estimate if your cycles do not run like clockwork.
How is an IVF due date different from a natural conception due date?
An IVF due date starts from a known embryo age at transfer rather than an estimated ovulation date, so it tends to be more precise. The Day 3 versus Day 5 distinction matters here too, since a Day 5 embryo is already two days older at transfer than a Day 3 one.
Why does my due date change after an ultrasound?
Early ultrasounds measure the pregnancy directly, which is generally more accurate than a last-period estimate, especially if your cycles are irregular or you are not entirely sure of your last period date.
It is common and expected for a scan to shift your due date by a few days from an initial last-period estimate. A shift of more than a week or so is worth asking your provider about, simply for your own understanding.
What is a due date actually for, if most babies do not arrive on it?
It marks 40 weeks, a useful midpoint for planning leave, appointments, and a general sense of timing, rather than a firm deadline. A full-term range runs from about 37 to 42 weeks, so the due date is really the center of a window, not the edge of one.
About Emma Bennett
Emma Bennett
I am a blogger, not a doctor or a health professional. I built Luna from my own cycle tracking, and this calculator grew out of the same instinct, wanting a clear answer instead of a vague one when the question changed from “when will I ovulate” to “when am I due.” I wrote this guide from that practical, been-there side, checked against trusted health sources for anything clinical. You can read more about my background on the about page.
Please read: This calculator and article are for general education and personal planning. They offer estimates, not medical advice. Due dates shift for good reasons, and only your provider can give you a personalized one. For any concern about your pregnancy, timing, or dating, please speak with a qualified healthcare provider.
Sources I leaned on
I am not a clinician, so I cross-checked the clinical points in this guide against well-regarded health organizations. If you want to read further, these are good, trustworthy places to start:
