Due Date Planning Guide
Why the Date Matters
A due date is an estimate, not a guarantee. It gives a helpful planning point for checkups, scans, leave dates, and birth preparation. Most pregnancies are dated from the first day of the last menstrual period. That method assumes ovulation near day fourteen of a twenty eight day cycle. Real cycles can be shorter or longer, so this calculator lets you adjust cycle length.
Last Period Equation
The main equation adds two hundred eighty days to the last menstrual period. This is often called Naegele style dating. If the cycle length is not twenty eight days, the difference is added or removed. A thirty day cycle adds two days. A twenty six day cycle removes two days. This keeps the estimate closer to the likely ovulation day.
Other Dating Methods
You can also calculate from conception. In that case, the equation adds two hundred sixty six days. This matches the usual time from ovulation to the estimated delivery date. For fertility treatment, the transfer day matters. A three day embryo transfer adds two hundred sixty three days. A five day transfer adds two hundred sixty one days. These values adjust for embryo age.
Using Scan Details
Ultrasound dating uses the scan date and gestational age on that day. The calculator converts weeks and days into total days. Then it subtracts that age from two hundred eighty days. The remaining days are added to the scan date. This can be useful when periods are irregular or unknown.
Reading the Result
The result also shows trimester dates, current pregnancy age, and days remaining. These details support planning, but they should not replace medical advice. Doctors may change the official date after early ultrasound, clinical history, or fertility records. Use this tool for education, comparison, and preparation. Always follow your healthcare provider for final pregnancy dating.
Because every pregnancy is individual, the final date is best treated as a range. Many births happen before or after the estimate. Tracking the method, source date, and cycle assumption makes the number easier to review later. Save the CSV or PDF when you need a simple record for personal notes, family planning, or appointment discussions. Keep earlier records for comparison during later prenatal visits with your clinician too.