Due Date Calculator

What is the Due Date Calculator?

The Due Date Calculator is a free online tool that estimates when your baby is likely to be born and tells you how far along you already are. Instead of forcing one fixed method, it lets you start from whichever date you actually know: the first day of your last menstrual period, the day you conceived or ovulated, or the day of an IVF embryo transfer. From that single input it works out your estimated due date, your current gestational age in weeks and days, the trimester you are in, your estimated conception date, and a simple countdown of how long is left to go. Everything is calculated instantly in your browser, so it is the kind of answer you get in a second and then carry on with your day.

How to use it

1. Choose how you want to calculate — from your last period, your conception or ovulation date, or your IVF transfer.
2. Pick the relevant date in the date field. The label updates to match the method you selected.
3. For the last-period method, set your average cycle length if it is not the standard 28 days. For IVF, choose whether a day-3 or day-5 embryo was transferred.
4. Read the answer instantly — your estimated due date appears in the headline, with gestational week, trimester, conception date and time-to-go below it.
5. Tap "Copy result" if you want to save or share the summary. That is the whole flow, and you can close the tab.

The method behind it

The three methods all converge on the same answer because pregnancy length is well established. A full-term pregnancy lasts about 280 days, or 40 weeks, measured from the first day of the last menstrual period.

• From the last period (Naegele's rule) — the classic rule takes the first day of your last period, adds one year, subtracts three months and adds seven days, which is the same as adding 280 days. If your cycle is longer or shorter than 28 days, ovulation shifts, so the calculator adds your cycle length minus 28 to keep the estimate honest.
• From conception or ovulation — conception happens roughly 14 days after the last period in a standard cycle, so a known conception date is dated at 280 minus 14, which is 266 days to the due date.
• From an IVF transfer — the fertilisation date is known precisely. A day-5 blastocyst is already 5 days along, so the tool adds 261 days; a day-3 embryo adds 263 days. This is why the embryo age matters.

Once the due date is fixed, gestational age is simply the number of whole days between the dating start point and today, shown as weeks plus days, and the trimester is read off that week count.

Worked examples

• Last period — a last period starting 1 January 2026 with a 28-day cycle gives an estimated due date of 8 October 2026 (280 days later).
• Longer cycle — the same 1 January 2026 start with a 32-day cycle pushes the due date to 12 October 2026, four days later, because ovulation was four days later.
• IVF blastocyst — a day-5 embryo transferred on 1 February 2026 gives a due date of 20 October 2026 (261 days later), with conception counted from the transfer.

Common use cases

• Planning ahead — booking time off, classes, or travel around an expected arrival.
• Tracking progress — checking which week and trimester you are in to follow milestones and appointments.
• IVF and fertility journeys — getting a precise due date from a known transfer date rather than a fuzzy period estimate.
• Sharing news — copying a clean summary to send to a partner, family or your care team.

Why use this one

Many due date pages only ask for your last period and give a single date. This one supports three starting points, adjusts for cycle length, and handles day-3 versus day-5 IVF embryos, so the estimate fits your actual situation instead of assuming a textbook 28-day cycle. It also goes beyond the due date itself by showing your gestational week, trimester, estimated conception date and a countdown in one view. It runs entirely in your browser using your device clock, there is no account, and your pregnancy details never leave your device.

It belongs to a small cluster of everyday date tools. To measure the exact gap between any two dates, use the Date Difference Calculator; to turn a birth date into an exact age once your baby arrives, use the Age Calculator; and to watch the days tick down to your due date live, the Countdown Timer does it in real time.

Frequently asked questions