About the Pregnancy Calculator
Pregnancy Calculator helps estimate the key numbers involved in pregnancy decisions. It is designed for quick scenario comparison: enter a realistic set of values, calculate the result, then change one assumption at a time to see what has the greatest effect. Unlike a static table, the result responds to your inputs and keeps the calculation in your browser. Health and fitness results are population-based estimates. They can support a conversation or planning process, but they do not determine an individual diagnosis, treatment, or safe activity level.
How to use this calculator
Enter values that match your situation and select Calculate result. Review the main result and its supporting figures, then change one input at a time to compare scenarios. Results are rounded for readability while the calculation retains additional precision internally.
Information you will need
- Calculation Method
- Date
- Cycle Length
- Ultrasound Weeks
- Embryo Age
How the calculation works
Calculate due date and gestational age from 5 methods: Last Period, Due Date, Conception Date, Ultrasound Date, or IVF Transfer Date. Read the primary result together with the supporting values rather than focusing on one number alone. A useful estimate should make its assumptions visible. If the answer looks surprising, verify the unit, rate, time period, and whether the entered value is gross or net. Run a conservative and an optimistic scenario to understand the range of possible outcomes.
Formula or method
Due = LMP + 280 days (40 weeks). Gestational age from LMP. Cycle length adjusts for variations.
Worked example
Enter any date to calculate due date and current week.
The example is illustrative rather than a recommendation. Use your own verified values and keep all monetary or measurement units consistent. When comparing alternatives, save or note each result so the assumptions do not become mixed.
How to interpret the result
The primary output answers the main question posed by the pregnancy calculator, while the additional cards provide context. A result with many decimal places is not necessarily more certain. The displayed precision makes comparison easier, but uncertainty in the inputs can be larger than the rounding difference.
Look for trends and ranges instead of treating a single estimate as a pass or fail result. If the output conflicts with symptoms, professional advice, or a direct measurement, rely on appropriate professional assessment.
Limitations and important notes
The pregnancy calculator cannot account for every factor that affects an individual result. Measurement technique, hydration, body composition, medication, pregnancy, illness, training status, and normal biological variation may matter. Do not use an estimate to diagnose a condition, select medication dosage, decide whether to drive, or ignore symptoms. A qualified professional can interpret measurements in the context of history and appropriate testing.
Frequently asked questions
How many weeks pregnant am I?
Gestational age is counted from the first day of your last menstrual period (LMP), not from conception. Enter your LMP and cycle length and the calculator counts the days between that date and today, dividing by 7 to give weeks plus leftover days. Because this system starts pregnancy about two weeks before conception, you are considered roughly two weeks pregnant at ovulation. If your dates or cycle length are uncertain, an early ultrasound can confirm dating. Remember this is an estimate, and your healthcare provider is the best source for your official dates.
Why is pregnancy counted from my last period instead of conception?
Because the exact day of conception is rarely known. Sperm can survive for several days inside the body and ovulation timing varies, so providers use a reliable anchor: the first day of your last period. They count 280 days (40 weeks) forward from that date. In this system pregnancy begins about two weeks before fertilization, which is why you can be told you are '2 weeks pregnant' before conception has even happened. If you conceived through IVF, your clinic can date the pregnancy precisely from the embryo transfer date.
How many months pregnant am I?
Months are uneven (28-31 days), so pregnancy is measured in weeks rather than months. Forty weeks equals roughly nine calendar months. A common mapping: weeks 1-4 are month 1, weeks 5-8 month 2, weeks 9-13 month 3, weeks 14-17 month 4, weeks 18-22 month 5, weeks 23-27 month 6, weeks 28-31 month 7, weeks 32-35 month 8, and weeks 36-40 month 9. Different calculators round slightly differently, so always go by weeks when discussing dates with your care team.
Which trimester am I in?
Pregnancy is divided into three trimesters of roughly 13 weeks each. The first trimester runs from week 1 through week 13, the second from week 14 through week 27, and the third from week 28 until birth (about weeks 28-40). Some sources shift these boundaries by a week or two, which is normal. Your calculator shows your trimester alongside your current week, and your provider will use it when scheduling ultrasounds, screenings, and tests, so mention your current week and trimester at appointments.
Why do my calculator and pregnancy app give different due dates?
Small differences usually come from the cycle length assumed. Many apps default to a 28-day cycle with ovulation on day 14; if you entered a 30- or 35-day cycle, ovulation and conception shift later, which moves the due date forward. Ultrasound dating can also adjust it by several days. Differences of a few days are completely normal and nothing to worry about. Only a healthcare provider should formally change a due date, and they typically do so only when a first-trimester scan disagrees by more than 5-7 days.
Can I use a pregnancy calculator if I have irregular periods?
Yes, but results are less reliable. The standard method assumes ovulation happens about 14 days before your next period, which is hard to predict when cycles are irregular. Your best estimate uses the cycle length you have observed, but the error grows as cycles vary. Ultrasound dating is far more accurate in this situation, since it measures the embryo rather than guessing ovulation. Treat any calculated date as a rough guide, and let your provider confirm dating with a scan at your first prenatal visit.
What week am I if I know my conception date?
Pregnancy is dated from your last period, not from conception, so a conception date converts by adding about two weeks: if you conceived eight weeks ago, you are roughly ten weeks pregnant. You can also add 266 days (38 weeks) to a known conception date to estimate your due date. This works best when ovulation is actually confirmed, such as with temperature tracking, ovulation tests, or IVF dates. Otherwise the conversion is an estimate, so confirm your dates with your healthcare provider.