Conception Date Calculator
Enter your estimated due date or the first day of your last period and we'll estimate when conception likely happened. It's a guide, not an exact answer. General information, not medical advice.
Pick a date above to see your estimated conception date.
General information, not medical advice.
How it works
Pick which date you already know — your estimated due date or the first day of your last menstrual period (LMP) — then choose it on the calendar.
From a due date, we count back about 266 days (38 weeks), since conception usually happens roughly two weeks after the start of your last period. From an LMP date, we add about 14 days, which is when ovulation and conception typically happen in an average cycle.
We also show a short fertile window around that date, because the exact day can shift depending on your cycle. Use it as a friendly estimate, not a definite date.
Frequently asked questions
How accurate is the conception date? +
It's an estimate. Conception is usually dated from ovulation, which can vary by several days from one person or cycle to the next, so treat the result as an approximate window rather than a fixed day.
Why is conception about two weeks after my last period? +
Pregnancy is counted from the first day of your last period, but you don't actually conceive until you ovulate — around day 14 in an average 28-day cycle. That's why the conception date lands roughly two weeks later.
Should I use this for legal or medical purposes? +
No. This is general information to satisfy curiosity. For anything official or medical, talk to your doctor or midwife, who can use ultrasound and your full history for a more precise date.
More tools for this stage
Weeks to Months Converter
Turn pregnancy weeks into months, weeks left, and your trimester.
Open tool →Due Date Calculator
Find your estimated due date from your last period or conception date.
Open tool →Pregnancy Calendar
Turn your due date into a calendar of scans, milestones and the big day — add it to Apple, Google or Outlook.
Open tool →