🤰 Free Pregnancy Calculator

A pregnancy calculator is a free online tool that estimates your due date, current pregnancy week, and trimester based on the first day of your last menstrual period (LMP) and your average cycle length. Instead of doing the date arithmetic by hand or second-guessing a calendar app, it gives you a clear timeline in seconds: expected delivery date, how many weeks pregnant you are today, which trimester you are in, an estimated conception window, and how many days remain.

The estimate is built on Naegele’s rule, the standard method clinicians have used for decades: add 280 days (40 weeks) to the first day of your last period. If your cycles are longer or shorter than the classic 28 days, the calculator adjusts the due date accordingly, which is why two people with different cycle lengths can get different dates from the same LMP.

Please remember this tool is for planning reference only and is not medical advice. Your doctor or midwife will confirm the timeline with an ultrasound, which remains the most accurate way to date a pregnancy.

The calculator applies Naegele’s rule: due date = LMP + 280 days + (cycle length − 28) days. The 280 days represent 40 weeks, the average length of a full-term pregnancy counted from the first day of the last period rather than from conception. Because ovulation typically happens about 14 days into a 28-day cycle, the actual embryo age at the due date is roughly 38 weeks; pregnancy simply counts from LMP, which is easier to know with certainty.

Your current week of pregnancy is calculated by counting the number of days between the LMP and today, dividing by 7, and adding 1—this is why the first week of pregnancy begins before conception has even occurred. The trimester is derived from the week: weeks 1–13 are the first trimester, weeks 14–27 the second, and weeks 28–40 the third. The cycle-length adjustment matters most for people whose cycles differ from 28 days: a 35-day cycle shifts ovulation and therefore the estimated due date about a week later.

All of this happens locally in your browser; no data is uploaded. The result is a well-established estimate, not a diagnosis. An ultrasound performed early in pregnancy remains the gold standard for dating, and your provider may adjust the date if measurements suggest a different gestational age.

People reach for a pregnancy calculator at the very moment they see a positive test, often before they have seen a doctor. It answers the first questions that come to mind: when is the baby due, how far along am I, and what should happen next. Common situations include:

• Sharing the news: telling family and friends “I’m 9 weeks pregnant” or “the baby is due in October” is far more concrete than guessing.
• Planning appointments: knowing your week helps you schedule the first prenatal visit, the anatomy scan around weeks 18–22, and other screening tests at the right time.
• Tracking progress: between checkups, a quick calculation shows which trimester you are entering and roughly how much time remains.
• Understanding the timeline: seeing that pregnancy is counted from the LMP explains why you are “2 weeks pregnant” before conception and makes medical discussions easier to follow.
• Comparing cycle lengths: if your cycles are irregular or longer than 28 days, the calculator shows how that changes the expected due date.

In every case, the tool is a planning aid. It turns a confusing date into a clear timeline and helps you walk into your first appointment with better questions. It is also useful for partners, family members, and birth-planning conversations: everyone can see the same projected dates and coordinate time off, travel, childcare for older siblings, and other practical arrangements around a shared estimate.

Because the calculator runs entirely in the browser, it is private by design. You do not need to create an account, share your name, or upload any health information, which matters to people who are still deciding who to tell about the pregnancy. You can also run it repeatedly as the date changes or as you learn your cycle better, and each run gives you a fresh, consistent timeline without any historical data being stored.

Example 1: Standard 28-day cycle. Your LMP was January 1. Add 280 days: January 1 + 280 days = October 8. The calculator shows a due date of October 8, current week and trimester based on today’s date, and a conception estimate around January 15 (about two weeks after the LMP). If today is March 1, the days since LMP equal 60; 60 ÷ 7 = 8 full weeks, plus 1 = week 9, which falls in the first trimester.

Example 2: Longer 35-day cycle. The same LMP of January 1 with a 35-day cycle shifts ovulation later by 7 days, so the due date becomes October 15 instead of October 8. This is the cycle-length adjustment built into the tool: (35 − 28) = 7 extra days added to the 280-day base. The current week calculation also shifts slightly because the extra days are included in the count from LMP.

Both examples produce estimates, not certainties. Only about 5% of babies arrive exactly on the due date; treat the number as the center of a two-week window rather than a promise.

Entering the conception date instead of the LMP. The tool expects the first day of your last period. If you enter the day you think conception happened, the due date will come out roughly two weeks too early. Conception occurs about 14 days after the LMP in a 28-day cycle, so keep the two dates straight.

Using a single unusual cycle length. If your cycles vary between 26 and 34 days, entering 34 once will push the date later than your average. Use a value close to your typical cycle, ideally averaged over a few months, and remember irregular cycles make every estimate less precise.

Treating the due date as exact. A due date is an estimate at the center of a normal range. Babies born between 37 and 42 weeks are generally considered full term, so panicking when the date moves by a few days is unnecessary.

Ignoring the ultrasound. The calculator uses dates; an early ultrasound uses measurements. If your provider adjusts the date, trust the clinical assessment over the calculator.

1. Enter the first day of your last period.
2. Set your average cycle length.
3. Click Calculate to see due date and progress.

How is my due date calculated?

Your due date is calculated using Naegele's rule: take the first day of your last menstrual period (LMP) and add 280 days, which equals 40 weeks. The calculator also adjusts for your average cycle length, and an ultrasound performed early in pregnancy may refine the date.

How many weeks pregnant am I from my LMP?

Count the full weeks from the first day of your last menstrual period to today. For example, if 60 days have passed since the LMP, you are 8 full weeks plus a few days pregnant, usually reported as 9 weeks.

Is the due date exact?

No. Only about 5% of babies arrive exactly on their due date. The due date is the center of a normal 37 to 42 week window, so think of it as an estimate for planning, not a guaranteed date.

Can I calculate from conception date instead?

Yes, you can add 266 days (38 weeks) from the estimated conception date. However, dating from the LMP is more common because the LMP is usually known with certainty, while ovulation and conception dates are harder to pin down.

Why does it say I'm 2 weeks pregnant before conception?

Because pregnancy weeks are counted from the first day of your last menstrual period, which happens about 2 weeks before ovulation and conception in a typical 28-day cycle. This is the standard medical convention, not an error.

When should I see a doctor to confirm?

Confirm the pregnancy with a home test first, then schedule a prenatal visit with a healthcare provider, who can arrange an early ultrasound to date the pregnancy accurately. This tool is for planning reference only and is not medical advice.

Use the due date to plan, not to worry. Book your first prenatal appointment as soon as you confirm the pregnancy and take the calculator’s estimate with you. Schedule key screenings around the weeks shown in the Reference Table, and note that the anatomy scan usually happens between 18 and 22 weeks.

Track your symptoms and milestones in a simple log; trends matter more than a single day. If your cycles are irregular, record the start dates of several periods before relying on any due date estimate. Remember that stress, travel, and illness can shift a cycle, so re-run the calculation if your LMP changes.

This tool is for planning reference only and is not medical advice. Always consult a qualified healthcare professional for prenatal care, and follow their guidance over any calculator output.