Pregnancy Due Date Calculator

How to use the pregnancy due date calculator

1. Pick the starting point you trust most: the first day of your last period, a conception date, an IVF transfer date, or a due date you already have.
2. Enter that date. For the last period method, also enter your usual cycle length if it is not 28 days. For an IVF transfer, choose the age of the embryo (day 3, 5 or 6).
3. Read the estimated due date, your gestational age in weeks and days, your trimester and the days left. The "Show my progress as of" date is today by default; change it to look at any other day.
4. Check the milestone timeline for approximate dates, then use "Print summary" or "Copy summary" if you want to keep the result.

How it works

A full pregnancy is counted as 280 days (40 weeks) from the first day of the last menstrual period, not from conception. Ovulation usually happens about two weeks later, so conception is typically about 266 days (38 weeks) before the due date. All four methods below end in the same kind of result, the estimated due date EDD.

• Last period: EDD = LMP + 280 + (cycle − 28) days. LMP is the first day of the last period and cycle is your average cycle length. The term cycle − 28 shifts the date when you ovulate earlier or later than day 14. This is Naegele's rule with a cycle adjustment.
• Conception date: EDD = conception + 266 days.
• IVF transfer: EDD = transfer + 263 days for a day 3 embryo, + 261 for day 5 and + 260 for day 6. The age of the embryo replaces the time that would otherwise pass between fertilisation and transfer.
• Known due date: the date is used as it is.

Gestational age on a chosen day is 280 − (EDD − that day) days, shown as whole weeks plus days (for example 15w0d). The trimesters follow the common convention: first through 13w6d, second from 14w0d to 27w6d, third from 28w0d. Dates are handled as plain calendar dates, so daylight saving time never moves a result by a day.

Examples

Example 1: last period. First day of last period 5 January 2026, cycle 28 days. EDD = 5 January 2026 + 280 days = Monday, October 12, 2026. On April 20, 2026 the pregnancy is 15w0d along, in the second trimester, with 175 days to go.

Example 2: longer cycle. Last period 1 March 2026, cycle 32 days. EDD = 1 March 2026 + 280 + 4 = 284 days = Thursday, December 10, 2026. On July 1, 2026 the result is 16w6d.

Example 3: conception date. Conception on 14 February 2026. EDD = 14 February 2026 + 266 days = Saturday, November 7, 2026. On June 15, 2026 the result is 19w2d.

Example 4: IVF. Day 5 embryo transferred on 10 May 2026. EDD = 10 May 2026 + 261 days = Tuesday, January 26, 2027. On August 1, 2026 the result is 14w4d, four days into the second trimester.

Weeks, trimesters and term

Pregnancy weeks are written as weeks and days: 14w0d means exactly 14 weeks and no extra days. Because the count starts at the last period, you are about "4 weeks pregnant" around the time a period is first missed in a 28-day cycle.

US obstetric guidance (ACOG) describes birth timing like this: early term is 37w0d to 38w6d, full term is 39w0d to 40w6d, late term is 41w0d to 41w6d and post-term is 42w0d and later. Only about 4 to 5 percent of babies arrive on the estimated date itself; most are born in the weeks around it. The calculator shows the term label once you reach 37 weeks.

Why your due date can change

• Irregular or long cycles. The last period method assumes ovulation about 14 days before the next period. If you ovulate later, the true date is later.
• Early ultrasound. A scan in the first trimester measures the embryo and is usually more precise than a remembered date. Clinics commonly keep the period-based date when the difference is small and move it when the gap is larger.
• Assisted conception. With IVF the transfer date is known exactly, so that method is usually the most precise.
• Multiple pregnancies. Twins and other multiples often arrive earlier, so clinics plan differently.

When your clinician gives you a date, choose "I already know my due date" and enter it. Their date, based on your history and scans, is the one to follow.

Using the result with your care provider

Bring the dates you used, especially the first day of your last period and your usual cycle length, to your first appointment. Mention a conception date or an IVF transfer date if you have one. Your provider can compare these with an ultrasound measurement and tell you which date will be used for your care. The printed summary is a convenient way to show what this page calculated, but the final date always comes from your clinician.

Frequently asked questions

How accurate is an estimated due date?

It is an estimate, not a prediction. Few babies are born on the exact day; a birth any time from 37 to 42 weeks is common. Treat the date as the middle of a window.

Which method should I use?

Use the date your clinician gave you if you have one. Otherwise an IVF transfer date is the most exact, then a known conception date, then the last period with your real cycle length.

Why does the calculator count from my last period if I conceived later?

Medical dating counts from the last period because that date is usually known, while conception is not. That is why a pregnancy is already about two weeks along at conception.

What if the result is not started yet, or shows more than 42 weeks?

If the "as of" date is before the pregnancy count starts, the page says so. More than 42 weeks usually means a date was typed wrongly, and the calculator asks you to check it.

Does this replace a visit to my midwife or doctor?

No. The page is general information. Tests, scans and the final date are decided by your care provider.

Is my data stored or sent anywhere?

No. The calculation runs in your browser and nothing is uploaded. The dates you enter are remembered only in your own browser's local storage so they are there when you return; you can replace them with "Reset to example" or by clearing site data.

This tool gives general information and an estimate only. It is not medical advice and does not replace a clinician. Contact your midwife or doctor with any concerns about your pregnancy.

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