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Browse all calculatorsEnter your last period, a conception date, an IVF transfer date or a due date to see weeks and days, trimester, estimated due date and a dated week table. An estimate only.
Only a midwife, doctor or an ultrasound dating scan can confirm how far along you are and when the baby is due. These dates are estimates for a typical cycle (28 days, conception around day 14). They cannot say how a pregnancy is going.
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 make any decision about your health care.
Each row is one week of gestational age, so the row for 8 weeks covers 8 weeks 0 days to 8 weeks 6 days, which many people call week 9. The highlighted row holds the date being counted to.
| Weeks | Dates | Tri | Notes from the sources |
|---|
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Count the days from the first day of your last period to today and divide by 7. The whole number is the weeks and the remainder is the days, so 60 days is 8 weeks 4 days. Pregnancy is counted as 40 weeks (280 days), so the estimated due date is that first day plus 280 days.
This pregnancy calculator does the sum for today or any date you choose, then adds the trimester, a countdown and a dated table of every week. Only a midwife, doctor or an ultrasound dating scan can confirm dates. For the due date by each method, see the due date calculator; for when conception most likely happened, see the pregnancy conception calculator. More everyday sums are in the free online calculators.
| Starting point | Date entered | Weeks and days | Due date |
|---|---|---|---|
| Last period, 28-day cycle | Jan 5, 2027 | 8 weeks 0 days | Oct 12, 2027 |
| Last period, 35-day cycle | Jan 5, 2027 | 7 weeks 0 days | Oct 19, 2027 |
| Conception date | Jan 19, 2027 | 8 weeks 0 days | Oct 12, 2027 |
| IVF transfer, day 5 embryo | Jan 24, 2027 | 8 weeks 0 days | Oct 12, 2027 |
| IVF transfer, day 3 embryo | Jan 22, 2027 | 8 weeks 0 days | Oct 12, 2027 |
| Due date | Oct 12, 2027 | 8 weeks 0 days | Oct 12, 2027 |
The first answer is already on screen. Change any value and the result, the schedule and the week table update at once, with no Calculate button.
Last period (with your cycle length), conception date, IVF transfer date with a day 3 or day 5 embryo, or a due date. Switching keeps the same pregnancy on screen.
Use the date picker or type YYYY-MM-DD. The form opens with an example date set 8 weeks 4 days back from today, so replace it with yours.
Weeks and days, the week number, trimester, estimated due date, days to go and the next date on the schedule appear under the inputs.
Scroll the dated table, change the date being counted to, copy the result, share a link with the same inputs or download a calendar file.
Days are counted from the count start. The labels are the ones the sources use; the notes below the table show where sources group weeks differently.
| Gestational age | Days from start | What the sources call it | Source |
|---|---|---|---|
| 0 weeks 0 days | 0 | Count starts: the first day of the last period | ACOG Committee Opinion 700 |
| 2 weeks 0 days | 14 | Conception is assumed around now, day 14 of the count | ACOG Committee Opinion 700 |
| 14 weeks 0 days | 98 | Second trimester begins (the first trimester ends at 13 weeks 6 days) | CDC, following ACOG |
| 28 weeks 0 days | 196 | Third trimester begins | CDC, following ACOG |
| 37 weeks 0 days | 259 | Early term begins (37 0/7 to 38 6/7) | ACOG Committee Opinion 579, via NICHD |
| 39 weeks 0 days | 273 | Full term begins (39 0/7 to 40 6/7) | ACOG Committee Opinion 579, via NICHD |
| 40 weeks 0 days | 280 | Estimated due date: 280 days after the first day of the last period | ACOG Committee Opinion 700 |
| 41 weeks 0 days | 287 | Late term (41 0/7 to 41 6/7) | ACOG Committee Opinion 579, via NICHD |
| 42 weeks 0 days | 294 | Post-term begins (42 0/7 and beyond) | ACOG Committee Opinion 579, via NICHD |
NHS week-by-week pages show the first trimester as ending at week 12, the second as weeks 13 to 27 and the third from week 28. This page follows the definitions the CDC uses, which follow ACOG, so the dates can differ from another source by a week or two. Your care team uses its own dates.
Many pages ask for one date and return a due date and a list of weeks. These are the differences that matter when you want to know where you are today.
| Feature | Basic pregnancy calculator | This calculator |
|---|---|---|
| Starting points | Often last period or due date only | Last period with cycle length, conception date, IVF day 3 or day 5 transfer, or due date |
| Where you are now | Often a due date and a table, leaving you to count | Weeks and days on today, or on any date you pick, with trimester and days to go |
| Week table | A list of weeks, sometimes with milestone notes that name no source | Dated rows from 0 to 42 weeks, the current row highlighted, notes only where an ACOG, NHS or CDC page states the window |
| Working | Answer only | Every input and each step of the sum, including the cycle adjustment |
| Results | Often a Calculate button | Updates as you type, with an answer on first load |
| Sharing | Rare | Copy the result, share a link with the same inputs, or download key dates as a calendar file |
| Care note | Often a footer disclaimer | A note beside the result that only a midwife, doctor or dating scan confirms dates |
Set the date to count to as the day of a visit or a scan, and the weeks, trimester and highlighted table row show where the count will be that day.
A scan report gives its own weeks and days. Enter the last period and the scan date to see how the two counts compare, then ask your midwife or doctor which date is used.
Enter the embryo transfer date and the age of the embryo, day 3 or day 5, to see the weeks and days the same way a clinic counts them.
If a scan or clinic has already given a due date, choose Due date to see the weeks and days today and the dated table. Compare dating methods in the due date calculator.
Download a calendar file with the estimated due date, trimester starts and term starts, or copy a summary to send to family. These are estimates, not appointments.
After the birth, the age calculator works out a baby age in months and days. Before pregnancy, the ovulation calculator covers cycle timing.
The count is a convention, not a measurement. These points come from the pages listed under Sources.
Only a midwife, doctor or an ultrasound dating scan can confirm dates. This calculator gives estimates for a typical cycle. It cannot say how a pregnancy is going, and it does not diagnose anything. If you are worried about your health or the pregnancy, contact your midwife, doctor or local emergency number.
ACOG states that by convention the due date is 280 days after the first day of the last menstrual period, assuming a regular 28-day cycle with ovulation on day 14. The first two weeks are counted before conception usually happens.
A 2016 study in Archives of Gynecology and Obstetrics notes that only 10 percent of women with a regular 28-day cycle ovulate on day 14. Cycle timing is covered in the ovulation calculator.
A 2013 study in Human Reproduction that timed ovulation reports that only 4 percent of women deliver at 280 days, with a 37-day range in the length of pregnancy even after excluding six preterm births.
ACOG describes when a scan date replaces a last-period date, starting at a gap of more than 5 days before 9 0/7 weeks and more than 7 days before 14 0/7 weeks. NHS says the 12-week scan may adjust the due date.
The CDC definitions used here, which follow ACOG, start the second trimester at 14 weeks 0 days. NHS pages list it from week 13. Check the dates your own care team uses.
A count of 8 weeks 4 days means 8 weeks are complete and the 9th week is under way, which is why the table shows both the weeks and the week number. For weight-change guidance by stage, see the pregnancy weight gain calculator.
It counts days from a date you type. It does not assess a pregnancy, a symptom or a test result, and it does not say whether anything is ahead of or behind a schedule. A midwife or doctor does that.
The 280-day count assumes a 28-day cycle. NHS says to adjust the cycle length, but neither NHS nor the ACOG opinion states by how much, so this page shifts the date by cycle length minus 28 days as a rule of thumb. If you do not know the date of your last period, NHS suggests speaking to a midwife or GP.
Notes in the table come from the pages linked under Sources and show the windows those pages state. They are not a care plan or a reminder service. Your midwife or doctor sets what applies to you.
The 280-day count, the 28-day and day 14 assumption, the IVF figures and the scan thresholds come from ACOG Committee Opinion 700. The acog.org page did not load for the tool used to read it, so its text was read through an archived copy of the same page. Trimester definitions come from a CDC page that follows ACOG, and term names from ACOG Committee Opinion 579 as restated by NICHD. Scan and vaccine windows are quoted from the NHS and CDC pages named here. The cycle adjustment of cycle length minus 28 days is a common rule of thumb that none of these pages sets out.
Short answers about weeks, trimesters, due dates and the limits of this calculator.
Count the days from the first day of your last period to the date you want and divide by 7. The whole number is the weeks and the remainder is the days, so 60 days is 8 weeks 4 days. This calculator does the sum for today or any date you pick, and it also works from a conception date, an IVF transfer date or a due date.
The standard method starts at the first day of the last menstrual period. ACOG states that by convention the due date is 280 days after that day, and that this assumes a regular 28-day cycle with ovulation on day 14, so conception is taken to happen about two weeks into the count.
By convention it is 280 days (40 weeks) after the first day of the last menstrual period. A last period starting on Jan 1, 2026 gives Oct 8, 2026. A conception date plus 266 days gives the same date, because conception is assumed 14 days into the count, and a day 5 or day 3 IVF transfer plus 261 or 263 days does too.
The 280-day count assumes a 28-day cycle, and ACOG notes that it does not account for irregular cycles or for variation in when ovulation happens. NHS says to adjust the cycle length if yours differs, without saying by how much. This calculator moves the date by the number of days your cycle differs from 28, a common rule of thumb, so a 35-day cycle moves the due date 7 days later. A scan gives a better date.
Following the definitions the CDC uses, which follow ACOG, the first trimester runs to 13 weeks 6 days, the second from 14 weeks 0 days to 27 weeks 6 days and the third from 28 weeks 0 days until delivery. NHS week-by-week pages group the weeks slightly differently, so a trimester date from another source can differ by a week or two.
Yes. Choose IVF transfer, enter the transfer date and pick a day 3 or day 5 embryo. ACOG says the due date is assigned from the age of the embryo and the date of transfer, which is 261 days from a day 5 transfer and 263 days from a day 3 transfer. Your clinic confirms your own dates.
It is an estimate. A 2013 study in Human Reproduction that timed ovulation states that only 4 percent of women deliver at 280 days, and it found a range of 37 days in the length of pregnancy even after excluding six preterm births. Treat the date as one point in a wide range and ask your midwife or doctor about your own dates.
A scan measures the baby, while the last-period method depends on remembering the date and on a regular cycle. ACOG says a scan before 9 0/7 weeks that differs from the last-period date by more than 5 days, or before 14 0/7 weeks by more than 7 days, is a reason to change the due date, with larger gaps allowed later. NHS says the 12-week scan may adjust the date. Your midwife or doctor decides which date is used.
Some calculators list the due date as the last day of week 40, which is day 279 of the count. This one follows the ACOG convention of 280 days after the first day of the last period, so the due date is 40 weeks 0 days.
Yes. Change Count to this date to an appointment day, a holiday or any other date, and the weeks, trimester, days to go and the highlighted table row update. Press Today to go back to the current date.
No. Everything runs in your browser and nothing is sent to a server. The date appears in the page address only after you change a value or tap Share link, so a shared link contains the date you typed.