Pregnancy Calculator
Find your estimated due date, how many weeks pregnant you are, the trimester and week-by-week development from your last menstrual period.
If your cycle is irregular, the results are an approximate estimate. Ultrasound measurements may be more accurate.
Knowing your due date, find which gestational week you're in and your estimated last period date.
This free, detailed pregnancy calculator lets you calculate pregnancy week by week from your last menstrual period: find your estimated due date, see how many weeks and months pregnant you are, and follow the trimester and baby development. As a pregnancy week calculator and gestational week calculator, it also works as a due date calculator and answers "how many weeks pregnant am I" and "how far along am I" in seconds. It is for information only and does not replace a doctor's care.
Pregnancy Calculator: How to Find Your Due Date
This pregnancy calculator finds your estimated due date, your gestational week and your trimester in seconds from your last menstrual period (LMP). When you want to calculate pregnancy dates, the calculation is based on Naegele's rule, the medical standard: add 280 days (40 weeks) to the first day of your last period. If your cycle is not 28 days, the difference is corrected automatically — making this a due date calculator you can rely on.
For example, if your last period was January 1 and your cycle is 28 days, your estimated due date is October 7. With a 30-day cycle, 2 days are added, making it October 9.
How Many Weeks (and Months) Pregnant Am I?
The question "how many months pregnant am I" can be answered roughly by dividing the number of weeks by 4.3. But medicine measures pregnancy in weeks, not months. The reason is simple: calendar months range from 28 to 31 days, and that ambiguity causes confusion in doctors' notes and ultrasound reports. "Week 23", on the other hand, means the same thing everywhere. The table below compares pregnancy weeks with months:
| Week | Approx. Month | Trimester |
|---|---|---|
| Weeks 1–4 | Month 1 | 1st Trimester |
| Weeks 5–8 | Month 2 | 1st Trimester |
| Weeks 9–12 | Month 3 | 1st Trimester |
| Weeks 13–17 | Month 4 | 1st–2nd Trimester |
| Weeks 18–21 | Month 5 | 2nd Trimester |
| Weeks 22–25 | Month 6 | 2nd Trimester |
| Weeks 26–30 | Month 7 | 2nd–3rd Trimester |
| Weeks 31–34 | Month 8 | 3rd Trimester |
| Weeks 35–40 | Month 9 | 3rd Trimester |
How Is the Gestational Week Calculated?
To find the gestational week, divide the number of days between your last period and today by 7. The remaining days are added, giving "X weeks Y days". For example, if 73 days have passed since your last period, you are 10 weeks 3 days. The answer to "how long does pregnancy last" is 40 weeks as standard; births between weeks 37 and 42 are considered normal. The tool calculates this automatically and also shows your estimated conception date, days until birth and important pregnancy milestones.
"How many weeks pregnant am I" is answered by the same formula. For the reverse — finding your last period from a due date — the tool subtracts 280 days from the estimated due date, or calculates the days remaining from today to the birth. Both tabs give a full result.
How Many Weeks Are in Each Trimester?
Pregnancy is divided into three trimesters:
- 1st Trimester (weeks 0–13): the baby grows rapidly and all the basic organs begin to develop. This is the period of highest miscarriage risk; the baby is first seen clearly on the 12-week ultrasound.
- 2nd Trimester (weeks 14–26): the mother usually feels best. Baby movements begin to be felt, the detailed anomaly scan is done at week 20, and the sex can be found out.
- 3rd Trimester (weeks 27–40): the baby gains weight quickly and prepares for birth. Doctor visits become more frequent; from week 37 birth is considered "term".
Early Pregnancy Symptoms: What Are the Symptoms of Pregnancy?
A common question alongside the dates is "what are the symptoms of pregnancy" and "how do I know if I'm pregnant". Early pregnancy symptoms vary from person to person, but the most common pregnancy symptoms are:
- Missed period — the most obvious and first-noticed sign
- Nausea and vomiting — usually in the morning, starting around weeks 4–8
- Breast tenderness and growth — becomes noticeable in the first weeks
- Frequent urination — increased blood volume makes the kidneys work harder
- Extreme tiredness — caused by rising progesterone
- Sensitivity to smells — some smells become strongly unpleasant
- Light spotting (implantation bleeding) — as the fertilized egg implants in the uterine wall
So how to know if you are pregnant for sure? If you have several of these early pregnancy symptoms, a home pregnancy test is the first step. If it's positive, see an obstetrician as soon as possible — only a doctor can confirm a pregnancy.
How Accurate Is the Calculation?
A pregnancy calculation from the last period is quite reliable for women with a regular 28-day cycle. However, an irregular cycle, late ovulation or hormonal variation can affect it. The medical gold standard is the 11–14 week ultrasound, where the due date is determined to within ±3–5 days using the baby's crown-rump length (CRL). This tool is for information only; consult your doctor for exact information.
In women with an irregular cycle — for example with Polycystic Ovary Syndrome (PCOS) — ovulation timing varies greatly, which can throw off the LMP-based calculation by several weeks. Likewise, in pregnancies through IVF the embryo-transfer date is known precisely, allowing a more accurate calculation; in these cases the doctor usually uses their own method based on the transfer date rather than the standard formula. So the LMP calculation is a starting point; the final gestational week and due date should always be confirmed by ultrasound.
Important Check-ups and Test Dates in Pregnancy
Routine check-ups and tests recommended at certain weeks are critical for both mother and baby:
- Weeks 11–14 — 1st-trimester ultrasound and screening: the baby's nuchal translucency (NT) is measured and a combined test (ultrasound + blood) screens for Down syndrome and other chromosome abnormalities. This ultrasound is also when the due date can be set most reliably.
- Weeks 18–22 — detailed ultrasound (anomaly scan): all of the baby's organ systems are examined in detail; the heart, brain, kidneys and spine are assessed. The sex can also be found out at this stage.
- Weeks 24–28 — gestational diabetes (GDM) screening: a glucose tolerance test (OGTT) checks for gestational diabetes. Early diagnosis prevents complications through diet or insulin.
- Weeks 35–37 — Group B Strep (GBS) test: a vaginal and rectal swab screens for Group B Streptococcus. A positive result means antibiotics during labour to prevent transmission to the newborn.
- Post-birth growth tracking: after the baby is born, percentile charts are used to track healthy growth.
How to Use This Pregnancy Calculator
This tool is very easy to use. Enter your last period date, and the tool automatically shows your estimated due date (EDD), gestational week, how-many-months result and trimester. For week-by-week tracking, it provides week-specific baby development information and a check-up calendar. Share or copy the result to take to your gynecology appointments or share with family.
How to Calculate a Pregnancy Step by Step
- Find your last period date: the first day of your cycle is the starting point; Naegele's calculation cannot be done without it.
- Enter your cycle length: standard is 28 days; if it differs, set it between 21 and 35 with the slider and the tool corrects the difference automatically.
- Press "Calculate Due Date": the estimated due date, gestational week and trimester appear instantly.
- Review the baby development card and timeline: week-specific size and ultrasound dates are listed.
- Share or copy the result: use the copy/share buttons for your doctor's appointment or to share with family.
Frequently Asked Questions About the Pregnancy Calculator
A pregnancy lasts about 40 weeks (280 days), counted from the first day of your last period. From week 37 a birth is "term"; pregnancies beyond week 42 are post-term. Births before week 37 are preterm (early).
Divide the gestational week by about 4.33. Weeks 1–13 are months 1–3 (1st trimester), 14–26 are months 4–6 (2nd trimester), and 27–40 are months 7–9 (3rd trimester). Medicine uses weeks, not months; this tool shows both.
The gestational week is the number of days between your last period and today divided by 7. For example, if 70 days have passed, you are in week 10. Enter your last period date in the tool to see your current week instantly.
The estimated due date (EDD) is calculated with Naegele's rule: add 280 days (40 weeks) to your last period date. If your cycle is not 28 days, the difference is added or subtracted. The most reliable method is the baby's size from an 11–14 week ultrasound (CRL).
Early signs include a missed period, morning nausea, breast tenderness, frequent urination, extreme tiredness and sensitivity to smells. They usually begin around weeks 4–6. Take a pregnancy test to confirm, then see a doctor.
Most women do not know the exact conception date because ovulation varies from cycle to cycle. The last menstrual period is usually remembered precisely, so it is used as the starting point; adding 2 weeks to it estimates conception. Ultrasound confirms the calculation.
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