Frequently Asked Questions
Common questions about pregnancy calculations and timelines.
We offer four calculation methods: 1) LMP (Naegele's Rule), 2) Conception Date, 3) IVF Transfer (3-day or 5-day), and 4) Ultrasound (CRL). Each uses specific medical formulas to estimate the 40-week (280-day) mark of your pregnancy.
CRL stands for Crown-Rump Length. It's the measurement of the fetus from head to bottom during a first-trimester ultrasound. Because early growth is very consistent, CRL can date a pregnancy within 3-5 days, making it the most accurate method available.
After calculating your due date, scroll down to the 'Milestones' section. Click the 'Add to Calendar' icon next to any milestone to add it to your Google Calendar, or use the 'Download All' option to get an ICS file for your phone or desktop calendar.
Calculators provide an estimate. Only about 4-5% of babies are born on their exact due date. Most arrive within two weeks before or after. An early ultrasound dating scan is generally more accurate than the LMP method.
LMP stands for Last Menstrual Period. Doctors use the first day of your LMP to date pregnancies because most women know this date, whereas the exact date of ovulation/conception is often unknown. Pregnancy weeks are counted from the LMP.
In IVF, embryos are transferred after developing in a lab for either 3 or 5 days. We adjust for this 'head start' by adding 263 days to a 3-day transfer date and 261 days to a 5-day transfer date.
Yes. Your healthcare provider might change your due date if an early ultrasound (dating scan) shows the baby is significantly different in size than the LMP date suggests. Once established by an early scan, the date is rarely changed.
A pregnancy is considered 'full term' starting at 39 weeks. 'Early term' is 37 weeks to 38 weeks and 6 days. Babies born full term generally have the best health outcomes.
Schedule your first prenatal appointment, start taking prenatal vitamins, and use our 'Add to Calendar' feature to keep track of important milestones and scans throughout your journey.
Pregnancy is counted in completed weeks. If you are '12 weeks and 3 days' pregnant, it means you have completed 12 full weeks and are 3 days into your 13th week. Our calculator does this math for you automatically.