Pregnancy Week Calculator — How Many Weeks Pregnant Am I?
Enter the first day of your last period or your ovulation date to see today’s week and your progress at once.
Do you have ultrasound results? (optional)
Pregnant today
These results are estimates for reference only. Confirm your exact gestational age and due date with your doctor or midwife.
🔄 Reopen this page each week and it recalculates from today.
How to use
How pregnancy weeks are calculated
Pregnancy is counted in weeks and days since the first day of your last menstrual period (LMP), not from the day of conception. That surprises many people, because it means you are already counted as two weeks pregnant on the day you ovulate and conceive. This pregnancy week calculator takes either your LMP or your ovulation date, works out how many days have passed to today, and shows the result as weeks and days, together with your estimated due date, your trimester and a progress bar across the 40 weeks. If you have had an early ultrasound, you can enter its date and the gestational age it gave you to correct the dating.
The due date rule
The estimated due date comes from Naegele’s rule, which adds 280 days (40 weeks) to the first day of your last period. It assumes a 28-day cycle with ovulation on day 14. If your cycle is shorter or longer than 28 days, ovulation likely happens earlier or later, so the calculator adjusts the date by the difference. For example, a 32-day cycle moves your due date four days later. If you enter an ovulation date instead, the due date is 266 days (38 weeks) after ovulation, because conception happens right around ovulation.
Due date = first day of last period + 280 days | Due date = ovulation date + 266 days
Example: a last period that started on January 10 gives a due date of October 17 in a non-leap year. Only about 4 percent of babies are born on their due date, and most arrive within two weeks either side, so treat it as the middle of a window, not a deadline.
Trimesters and weeks
- First trimester: from the start of week 1 through week 13 and 6 days. Major organs form and the risk of miscarriage is highest. Prenatal care often begins around weeks 8 to 10.
- Second trimester: weeks 14 through 27 and 6 days. Many people feel better and first notice movement around weeks 16 to 22. A detailed anatomy ultrasound is usually done between weeks 18 and 22.
- Third trimester: week 28 until birth. Screening for gestational diabetes is commonly done at weeks 24 to 28, and the Tdap vaccine is recommended during weeks 27 to 36 of each pregnancy.
What counts as early, full and late term?
The American College of Obstetricians and Gynecologists (ACOG) uses four labels for birth timing: early term is 37 weeks 0 days through 38 weeks 6 days, full term is 39 weeks 0 days through 40 weeks 6 days, late term is 41 weeks 0 days through 41 weeks 6 days, and post-term is 42 weeks 0 days or later. Babies born full term generally have the best outcomes, which is why doctors avoid scheduling non-medical deliveries before 39 weeks. A baby born before 37 weeks is considered preterm. Ask your care team what timing makes sense for you.
Why an ultrasound can change your dates
The last-period method depends on remembering your date and having a regular cycle. An early ultrasound measures the embryo or fetus, and in the first trimester that measurement is the most accurate way to estimate gestational age, within roughly five to seven days. ACOG advises that your due date generally be changed to the ultrasound date if it differs from the last-period date by more than five days before 9 weeks, or by more than seven days between 9 and 16 weeks. This calculator lets you enter the ultrasound date and the weeks and days it reported, and it re-bases your dating, telling you how many days it shifted.
Weeks, months and why they do not match
Forty weeks is about nine months and one week, but the common “nine months” is only a rough guide because months differ in length. Providers use weeks for precision: a pregnancy measured as 27 weeks 3 days is in the second trimester and one week away from the third. If someone says you are “seven months,” they usually mean week 28 to 31.
A few milestones to look for
These are general landmarks, and your provider will tell you what applies to you. Around weeks 6 to 7, a heartbeat can often be seen on an early ultrasound. Week 12 is a common time for first-trimester screening. Week 20 is the halfway point and a typical time for the anatomy scan. Around week 24, a baby born early has a chance of survival with intensive care, and each additional week improves the outlook. By week 37 the baby is considered early term, and by week 39 full term.
Using the results
Write down the due date and today’s weeks and days so that you can compare them with what your care team tells you at appointments. If the dates differ, go with the provider’s dating, since they know your ultrasound results. For a different view of the same timeline, the Due Date Calculator shows key milestones and the Ovulation Calculator helps if you are still planning to conceive.
Frequently asked questions
How many weeks pregnant am I if I conceived today?
About two weeks. Pregnancy weeks are counted from the first day of your last period, which is roughly two weeks before ovulation and conception. If you know your ovulation date, choose the ovulation option and the calculator corrects for it.
How accurate is the due date?
It is an estimate. Only around 4 percent of babies arrive on the due date, and a healthy pregnancy can end anywhere from 37 to 42 weeks. Cycle length, how well you remember your last period and the baby’s own timing all matter.
What if I have irregular periods?
If your cycles vary a lot, the last-period method is less reliable. Enter your typical cycle length, or better, ask your provider for an early ultrasound, which can set your dating more accurately. You can then enter the ultrasound results here.
Why does my doctor’s due date differ from this one?
Your provider may have adjusted your dating using an ultrasound, or used a different cycle length. Go with your provider’s date. This tool is for planning and curiosity, not for medical decisions.
When does the first trimester end?
At the end of week 13 and 6 days; the second trimester starts at 14 weeks 0 days. The progress bar and the trimester card update automatically as the weeks pass.
Can I use my IVF transfer date?
IVF dating is different from natural conception. Use the dates from your clinic, because they calculate the due date from the embryo’s age at transfer. Enter their gestational age as an ultrasound reference if you want the weeks and days shown here.
Is my date stored anywhere?
No. The dates stay in your browser, nothing is sent to a server, and nothing is stored after you close the page.