Pregnancy Calculator: Due Date and Week by Week
Count from day one of bleeding to the day before your next period starts. Not sure? Leave it at 28.
Sperm can live up to five days, so the day you had sex and the day you conceived may differ.
Look for "GA" or "gestational age" on your scan report, written like 9w4d.
Handy for a wedding, a flight or a work deadline. Leave blank to use today.
Pick a date to see your results. Dates stay in your browser and are never sent anywhere.
Many calculators still use Naegele's rule: add a year, subtract three months, add seven days. We ran every possible start date from 2024 through 2026 through both that shortcut and a straight 280-day count. They matched only about 53% of the time and were off by up to three days, because calendar months aren't all the same length. This calculator counts days, adjusts for your cycle length, and switches to embryo-age math for IVF.
Two questions come first after a positive test: when is the baby due, and how far along am I right now? The calculator above answers both from your last period, conception date, IVF transfer or an ultrasound, then lays out every scan, test and vaccine window with your actual dates. Below that you'll find a week-by-week size guide and straight answers to what people search next, including whether any calculator can tell boy from girl.
Key Answers About Due Dates and Pregnancy Weeks
Short answers first. Each one is covered in more depth further down the page.
Add 280 days to the first day of your last period. If your cycle is longer or shorter than 28 days, move the date later or earlier by the difference; a 33-day cycle adds five days.
Pregnancy weeks are counted from your last period, not from conception, because that's the date most people know. Conception usually happens about two weeks later, so a positive test around your missed period already puts you near four weeks.
A little over nine calendar months, about nine months and one week. The month chart below shows which weeks fall in each month.
No. A study of about 2.8 million Swedish births found the popular Chinese lunar chart was right roughly half the time, the same as flipping a coin. A blood test from 10 weeks or the 18- to 22-week ultrasound can actually tell you.
On or after the day your period is due. According to the FDA, 10 to 20 out of every 100 pregnant people won't get a positive on the first day of a missed period, so a negative that early isn't final. Retest a few days later with first-morning urine.
An early ultrasound usually wins. Under ACOG guidance, a first-trimester scan replaces the period-based date when the two differ by more than 5 days before 9 weeks, or by more than 7 days from 9 weeks to the end of week 13.
Pregnancy, birth and postpartum care average more than $20,000 in total, according to Peterson-KFF, and people with insurance still pay about $2,743 out of pocket on average.
Week-by-Week Baby Size, With Pictures
Slide through the weeks to see the average size, weight and what's developing. The slider opens on your current week once you enter a date.
Reflexes appear: fingers can curl and the fetus may start sucking motions. For many people, nausea starts easing.
Your Prenatal Test and Vaccine Dates
These windows follow ACOG and CDC timing. Enter a date in the calculator and the third column fills in with your own calendar dates.
| Milestone | Week | Your dates | Status |
|---|
ACOG recommends Tdap in every pregnancy (ideally weeks 27–36), a flu shot in any trimester, a COVID-19 vaccine, and either the RSV vaccine at weeks 32–36 during September through January or an RSV antibody shot for the baby after birth. Federal advice on flu and COVID-19 shots in pregnancy has shifted lately, so bring questions to your appointment.
Pregnancy Months by Week
There's no official week-to-month chart, so different sites split the weeks a little differently. This is the most common breakdown. Your month is highlighted once you enter a date.
A quick sanity check on the "nine months" idea: 280 days divided by the average month length of about 30.4 days is 9.2 months. That extra week is why people at 36 weeks are told they're "in month nine" while still having a month to go.
Boy or Girl? What Can Actually Tell You
Gender predictor charts are fun, but none of them work better than chance. Before testing, the only honest odds are close to 50/50; U.S. births run about 105 boys for every 100 girls.
| Method | Earliest week | How reliable | Cost |
|---|---|---|---|
| Chinese lunar calendar | Any time | About 50%, a coin flip | Free |
| Heart rate, belly shape, cravings | Any time | No better than guessing | Free |
| Ramzi theory (placenta side) | ~6 weeks | Not supported by research | Free with a scan |
| Cell-free DNA blood test (NIPT) | 10 weeks | Very accurate, not perfect | Often covered; ask insurer |
| Anatomy ultrasound | 18–22 weeks | Usually clear if baby cooperates | Part of routine care |
Enter a date in the calculator and we'll show the earliest day a blood test could tell you and the week your anatomy scan is likely to fall.
The blood test's main job is screening for chromosome conditions; sex is a side result. If you'd rather be surprised, tell the lab and the sonographer before results come back, because it's easy to see on a printout.
How Accurate Is Your Due Date?
Every method gives an estimate. How good that estimate is depends on what it's built from.
| Method | How it's calculated | Accuracy | Best for |
|---|---|---|---|
| Last period | LMP + 280 days, ± cycle difference | Good with regular cycles | Most people, first estimate |
| Conception date | Conception + 266 days | Good if date is certain | Tracked ovulation |
| IVF transfer | Day-5: +261 · Day-3: +263 days | Most precise | Assisted reproduction |
| First-trimester ultrasound | Crown-rump length, up to 13w6d | Within about 5–7 days | Irregular cycles, unsure LMP |
| Later ultrasound | Head, belly, thigh-bone size | Less precise after 22 weeks | Late start to care |
Once your clinician sets a due date from the best early evidence, it usually shouldn't move. A later scan that measures "big" or "small" tells you about growth, not about a new due date. If you're handed a second date late in pregnancy, it's fair to ask which one your care team is using for decisions like induction.
What to Do in Your Situation
Apply for Medicaid now rather than waiting. Income limits for pregnant people are often well above the limits for other adults, many states offer presumptive eligibility so you can start prenatal care while the application is processed, and nearly every state now keeps postpartum Medicaid for a full year after birth. On HealthCare.gov, pregnancy by itself usually doesn't open a special enrollment period, but the birth does.
The FMLA gives up to 12 weeks of unpaid, job-protected leave if your employer has 50 or more employees nearby and you've worked there 12 months and at least 1,250 hours. Separately, the Pregnant Workers Fairness Act requires employers with 15 or more workers to make reasonable accommodations, like extra breaks, a stool, water at your station or a temporary lighter duty. A growing number of states add paid family leave on top. Use the full-term window above, not the single due date, when you tell your boss.
Use the IVF tab, not your last period. Your clinic knows the embryo's exact age, so the transfer date gives the most precise due date there is: 261 days after a day-5 transfer or 263 days after a day-3 transfer. If your clinic's paperwork shows a different date, trust theirs; some clinics date from egg retrieval instead.
A period-based date can be off by weeks if you ovulate late or irregularly, or if you're coming off birth control. Ask for a dating ultrasound before 14 weeks; it's the most accurate tool available after IVF. Then switch to the Ultrasound tab and enter the gestational age from the report.
Going a few days over is common, especially with a first baby. From 41 weeks, ACOG advises talking about induction, and many practices add monitoring visits. For healthy first-time parents, the large ARRIVE trial found that choosing induction at 39 weeks didn't raise the cesarean rate; it was 18.6% versus 22.2% with waiting. Ask your clinician which option fits your pregnancy.
Call 911 or get emergency care for chest pain, trouble breathing, a seizure, or thoughts of harming yourself or your baby. Call your provider right away for a headache that won't go away, vision changes, a fever of 100.4°F or higher, sudden swelling of the face or hands, heavy bleeding or leaking fluid, severe belly pain, or if the baby's movements slow down or stop. Those are among the CDC's urgent maternal warning signs, and they apply for a year after birth too. When you call, say you're pregnant or recently gave birth.
This calculator gives estimates for planning and education. It doesn't replace the due date your clinician sets or medical advice. Baby sizes are population averages; lengths are crown to rump through week 19 and head to heel from week 20. Statistics are from the most recent U.S. data available in October 2026. Dates you enter stay in your browser.
Key sources: American College of Obstetricians and Gynecologists · Centers for Disease Control and Prevention (NCHS provisional birth data, Hear Her) · U.S. Food and Drug Administration · Peterson-KFF Health System Tracker · Paediatric and Perinatal Epidemiology (2010)