Conception Calculator
Calculate How Many Weeks and Days Pregnant You Are Today
Use a due date, LMP, conception date, ultrasound age, or IVF transfer to estimate gestational age and trimester.
Dates are estimates for general information. They are not a diagnosis and do not replace dating by your prenatal or fertility care team.
How the Pregnancy Week Calculator Measures Gestational Age
Pregnancy weeks are measured as gestational age from the first day of the last menstrual period, or from an equivalent date established by ultrasound or assisted reproduction. This convention begins about two weeks before fertilization in a typical 28-day cycle, which is why someone can be described as two weeks pregnant around conception.
The calculator finds the equivalent LMP for the method selected, counts complete seven-day intervals to today, and displays the remaining days. A result of 9 weeks 4 days means nine full weeks have elapsed and the pregnancy is four days into the next week.
How to Calculate Pregnancy Weeks From Due Date or Last Period
From an established due date, the calculator subtracts 280 days to estimate the start of gestational age and then counts forward to today. From an LMP, it counts directly from the first day of bleeding and applies the entered cycle-length adjustment when estimating the due date.
Use the due-date method when your prenatal record already contains an official estimated due date. Use LMP when the first day is known and cycles are reasonably regular. If those results disagree, the online comparison does not determine which record is clinically correct.
Pregnancy Weeks From Conception, Ultrasound or IVF Transfer
A known conception date is converted to an equivalent LMP by subtracting 14 days. Ultrasound dating subtracts the reported gestational weeks and days from the scan date. IVF dating subtracts the embryo age from the transfer date to estimate fertilization, then subtracts another 14 days for the equivalent LMP.
These conversions allow all methods to display weeks and days on the same gestational-age scale. They do not make every input equally reliable. ACOG recommends using ART-derived dating for IVF pregnancies and identifies first-trimester ultrasound as the most accurate ultrasound method for establishing or confirming gestational age.
How to Read Pregnancy Trimester and Milestone Dates
The result labels the current trimester and shows reference dates for weeks 12, 20, 28, 37, and 40. These markers make a long pregnancy timeline easier to scan. They do not prescribe when a particular test, appointment, or delivery should occur because care schedules depend on clinical circumstances and local guidance.
If the calculated pregnancy has not started, the due date has passed, or the entered date describes a past pregnancy, the status is shown directly. The calculator does not assume that every historical or future date represents an ongoing pregnancy.
Pregnancy Weeks vs Months and Why the Counts Differ
Pregnancy care usually uses completed weeks and days because calendar months have unequal lengths. Converting weeks into a simple month number can create inconsistent answers: four weeks is 28 days, while most calendar months contain 30 or 31 days. This tool therefore keeps the primary result in gestational weeks and days.
Apps may also label the current week differently. At 9 weeks 4 days, nine weeks are complete, but the pregnancy is in its tenth week. Check whether another source reports completed weeks or the week currently in progress before treating a one-week wording difference as a dating conflict.
Sources for This Pregnancy Week Calculator Method
Our formulas and interpretation notes were reviewed against the following clinical and public-health references on August 2, 2026. These sources explain general dating methods and do not validate an individual result.
Frequently Asked Questions About Pregnancy Week Calculations
Why am I two weeks pregnant before the estimated conception date?
Gestational age is conventionally counted from the first day of the LMP, not from fertilization. That adds about two weeks before conception in a 28-day model.
How do I calculate pregnancy weeks from a due date?
Subtract 280 days from the due date to estimate an equivalent LMP, then count completed weeks and remaining days from that date to today.
What does 8 weeks 3 days pregnant mean?
It means eight complete weeks and three additional days of gestational age have elapsed. In conversational terms, you are in your ninth week of pregnancy.
Why does my ultrasound show a different pregnancy week?
Differences can reflect uncertain menstrual dates, cycle timing, measurement variation, or the stage of pregnancy. Ask your clinician which due date and gestational age should guide care.
Does the pregnancy timeline replace prenatal appointments?
No. Its milestones are general calendar reference points. A prenatal care professional should determine appointments, tests, and clinical timing for your circumstances.