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Browse all calculatorsEstimate a due date from your last period, conception date, IVF transfer or ultrasound scan, then see the early-term to post-term window.
Only a midwife, doctor or an ultrasound dating scan can confirm your dates. These are estimates for cycles of typical length, and few babies arrive on the exact day.
This is a general estimate for educational use. It is not medical advice, a diagnosis or a treatment plan. Talk to a doctor, midwife or other qualified professional before you change your health care or your plans for the birth.
| Method | Due date | Difference |
|---|
| Stage | Weeks | Dates |
|---|
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A due date calculator estimates when a baby is due by counting forward from a starting date. The last period method adds 280 days (40 weeks), adjusted for cycle length. A conception date adds 266 days, an IVF transfer counts from the age of the embryo, and an ultrasound scan uses the gestational age it reports.
This due date calculator puts all four methods in one place and shows them side by side, so you can see how far apart they land. It then marks the early term, full term, late term and post-term dates for the date you pick. To see how far along you are each week, with the full dated table, use the pregnancy calculator. To work backward from a due date, try the pregnancy conception calculator. For other everyday sums, see the free online calculators.
| Method | Date entered | Count | Due date |
|---|---|---|---|
| Last period, 28-day cycle | Jan 10, 2027 | + 280 days | Sun, Oct 17, 2027 |
| Last period, 32-day cycle | Jan 10, 2027 | + 280 + 4 = 284 days | Thu, Oct 21, 2027 |
| Last period, 24-day cycle | Jan 10, 2027 | + 280 – 4 = 276 days | Wed, Oct 13, 2027 |
| Conception date | Jan 24, 2027 | + 266 days | Sun, Oct 17, 2027 |
| IVF, day 5 embryo transfer | Jan 29, 2027 | + 261 days | Sun, Oct 17, 2027 |
| IVF, day 3 embryo transfer | Jan 27, 2027 | + 263 days | Sun, Oct 17, 2027 |
| Scan at 10 weeks 0 days | Mar 21, 2027 | + (280 – 70) = 210 days | Sun, Oct 17, 2027 |
The first answer is already on screen. Change any date and it updates at once, with no Calculate button.
Choose Period, Conceived, IVF or Scan. Use the one your records are based on. The last period method needs the first day of the last period and the cycle length.
Use the date picker or type the date as 2027-03-10. For IVF add the age of the embryo at transfer, and for a scan add the weeks and days it reported.
The big date is the estimated due date. Below it are your age in weeks and days today, the trimester, the days to go and the dates where early term, full term and post-term begin.
Tap Add on another method to see its due date next to the first and the gap in days. With a scan and a last period, the gap is set against the ACOG threshold.
Every method finds the same thing: the date that is 280 days after the start of the 280-day count, which is the first day of the last period for a regular 28-day cycle. The methods differ only in which date they start from. Ovulation falls about 14 days into a 28-day cycle, so a conception date is 14 days later than the start of the count and needs 266 days instead of 280.
Naegele's rule is the last-period method written as a formula. This page adds the cycle adjustment: a cycle longer or shorter than 28 days moves the date by the difference. All counts are whole calendar days, so nothing is rounded. For counting between two dates in general, see the age calculator.
| Method | Formula |
|---|---|
| Last period | First day of last period + 280 days + (cycle length − 28) |
| Conception date | Conception date + 266 days (38 weeks) |
| IVF, day 5 embryo | Transfer date + 261 days |
| IVF, day 3 embryo | Transfer date + 263 days |
| IVF, day 6 embryo | Transfer date + 260 days (266 − 6, the same rule as day 3 and day 5) |
| Ultrasound scan | Scan date + (280 − gestational age at the scan, in days) |
| Age today | Today − (due date − 280 days), shown as weeks and days |
These are the published figures the calculator uses. Weeks and days are written as 37w0d for 37 weeks 0 days. Each figure comes from a document listed under Sources.
| Stage | Weeks and days | Source |
|---|---|---|
| First trimester | up to and including 13w6d | ACOG Committee Opinion 700 |
| Second trimester | 14w0d to 27w6d | ACOG Committee Opinion 700 |
| Third trimester | 28w0d onward | ACOG Committee Opinion 700 |
| Early term | 37w0d to 38w6d | ACOG and SMFM, via NICHD |
| Full term | 39w0d to 40w6d | ACOG and SMFM, via NICHD |
| Late term | 41w0d to 41w6d | ACOG and SMFM, via NICHD |
| Post-term | 42w0d and beyond | ACOG and SMFM, via NICHD |
| Gestational age at the scan | Difference in days |
|---|---|
| 8w6d or less | more than 5 |
| 9w0d to 13w6d | more than 7 |
| 14w0d to 15w6d | more than 7 |
| 16w0d to 21w6d | more than 10 |
| 22w0d to 27w6d | more than 14 |
| 28w0d and beyond | more than 21 |
| Cycle length | Days added | Total count | Due date |
|---|---|---|---|
| 22 days | -6 | 274 days | Sat, Oct 2, 2027 |
| 24 days | -4 | 276 days | Mon, Oct 4, 2027 |
| 26 days | -2 | 278 days | Wed, Oct 6, 2027 |
| 28 days | 0 | 280 days | Fri, Oct 8, 2027 |
| 30 days | +2 | 282 days | Sun, Oct 10, 2027 |
| 32 days | +4 | 284 days | Tue, Oct 12, 2027 |
| 34 days | +6 | 286 days | Thu, Oct 14, 2027 |
| 36 days | +8 | 288 days | Sat, Oct 16, 2027 |
| 40 days | +12 | 292 days | Wed, Oct 20, 2027 |
| 44 days | +16 | 296 days | Sun, Oct 24, 2027 |
Many due date calculators take one date and return one date. These are the details that change what the date means.
| Feature | Basic due date calculator | This calculator |
|---|---|---|
| Methods | Often last period only | Last period with cycle length, conception date, IVF day 3, 5 or 6, and ultrasound |
| Results | Often needs a Calculate button | Updates as you type, with an answer on first load |
| After the date | One date and little else | Age today in weeks and days, trimester and days to go |
| Term window | Rarely shown | Dates for early term, full term, late term and post-term, with the week boundaries from ACOG and SMFM |
| Comparing methods | One method at a time | Methods side by side with the gap in days, and a scan checked against the last-period date using the ACOG threshold |
| Working and sources | Answer only, few links | Every step written out and every figure traced to a document |
| Sharing | Start again each time | Copy the result or share a link with the same dates |
Enter the last period and the scan together to see the gap in days and the ACOG threshold for that stage, then ask the midwife or doctor which date is used.
Pick the transfer date and the age of the embryo to see the date counted from the transfer, next to a last-period date if you have one.
Try a conception date or a scan result instead and compare. A scan is the way to confirm a date when the last period is uncertain.
Early term, full term, late term and post-term are easier to picture as calendar dates. The bar and the table show where each begins.
Use the pregnancy calculator for the week table and key dates, and the pregnancy weight gain calculator to compare weight with published ranges.
See ovulation timing with the ovulation calculator and upcoming dates with the period calculator.
A due date is an estimate built from published counting rules. It describes a typical pregnancy, not any one person, and a midwife or doctor decides which date is used for care.
A study quoted by Jukic and colleagues reported that only 4 percent of women delivered at 280 days and about 70 percent within 10 days of the estimated due date.
ACOG sets out when a scan date replaces a last-period date. The calculator shows the gap and the threshold and leaves the decision to your midwife or doctor.
Gestational age starts about 14 days before conception, so a pregnancy of 40 weeks is about 38 weeks from conception.
Only the last-period method uses it. A 32-day cycle moves the date 4 days later and a 24-day cycle moves it 4 days earlier.
The count runs from the transfer date and the age of the embryo, so there is no cycle to adjust for.
Nothing you type leaves your browser. After the page loads, the calculator keeps working without a connection.
Only a midwife, doctor or an ultrasound dating scan can confirm dates. This page gives estimates for cycles of typical length and is not medical advice. For the NHS version of the last-period method, see the NHS due date calculator.
It does not adjust for irregular cycles, for twins or more, or for a recent change in hormonal contraception. A midwife or doctor dates those pregnancies.
It does not predict ovulation or fertile days and it is not a way to avoid or plan a pregnancy. The ovulation calculator covers cycle timing.
The calculations are plain date arithmetic on the published rules, checked against hand-counted examples. The counting rules, week boundaries and statistics come from these documents.
Short answers to common questions about estimating a due date.
The usual method counts 280 days, which is 40 weeks, from the first day of the last menstrual period. ACOG says that by convention the estimated due date is 280 days after the first day of the last period. A last period that began on January 10, 2027 gives October 17, 2027. A scan or an IVF transfer date can be used instead when the last period is not known.
Take the first day of the last period, add 280 days and, if the cycle is not 28 days, add or remove the difference. A 32-day cycle adds 4 days, so a period that began on January 10, 2027 gives October 21, 2027. The NHS and March of Dimes calculators also ask for the cycle length when it is not 28 days.
Add 266 days, which is 38 weeks, to the conception date. That is the 280-day count minus the 14 days from the start of the last period to ovulation, the same step Jukic and colleagues use in their 2013 study. A conception date of January 24, 2027 gives October 17, 2027.
ACOG says the due date is assigned from the age of the embryo and the transfer date: 261 days after the transfer for a day 5 embryo and 263 days for a day 3 embryo. This calculator also offers day 6, using the same rule of 266 minus the embryo age, which is 260 days. Your clinic can confirm the date it uses.
In the last-period method it does. The 280-day count assumes ovulation on about day 14 of a 28-day cycle. A longer cycle puts ovulation later and moves the due date later by the same number of days, and a shorter cycle moves it earlier. This calculator accepts cycles of 22 to 44 days.
ACOG lists how far apart the two dates must be before the scan date is used: more than 5 days at 8 weeks 6 days or less, more than 7 days from 9 weeks 0 days to 15 weeks 6 days, more than 10 days from 16 weeks 0 days to 21 weeks 6 days, more than 14 days from 22 weeks 0 days to 27 weeks 6 days, and more than 21 days from 28 weeks 0 days. The calculator shows the gap and the threshold, and your midwife or doctor decides.
ACOG and SMFM defined early term as 37 weeks 0 days to 38 weeks 6 days, full term as 39 weeks 0 days to 40 weeks 6 days, late term as 41 weeks 0 days to 41 weeks 6 days, and post-term as 42 weeks 0 days and beyond. The calculator turns each range into dates for your due date.
Few. A 1996 ultrasound-dating study, quoted by Jukic and colleagues, reported that only 4 percent of women delivered at 280 days and about 70 percent within 10 days of the estimated due date. A due date works as a guide to the timing, not a deadline.
ACOG describes the first trimester as running up to 13 weeks 6 days, the second as 14 weeks 0 days to 27 weeks 6 days and the third as 28 weeks 0 days onward. The calculator shows yours from the date today, counted from the start of the 280-day count.
It does arithmetic on the date you enter, so it cannot know your cycle, your ovulation date or what a scan measured. Only a midwife, doctor or an ultrasound dating scan can confirm dates, and they decide which date is used for care.
No. The calculation runs in your browser and nothing is sent to a server. Your dates appear in the page address only so that a shared link opens with the same values.