The conception calculator estimates a reference conception date from a due date (about 266 days back) or last period (about +14 days)—not ultrasound dating.
How to use
- Pick due-date back-calculation or last-period mode.
- Enter the date.
- Cross-check with the due date calculator and gestational age tool.
More tools on the health hub. For planning reference only—not medical, nutrition, or obstetric advice.
Frequently asked questions
How is conception date estimated?
From due date (~266 days back) or last period (~+14 days)—average assumptions, often ± several days.
Use with due date calculator?
From LMP, get a due date on the due date calculator, then back-calculate here—or link to gestational age.
Ultrasound dates differ?
Early ultrasound often revises dating—follow clinical reports. This page is calendar math only.
Unsure of last period?
If you have a clinician due date, use due-date mode. Otherwise seek dating help—do not guess LMP.
Is this medical advice?
No—results are for planning reference only. See clinicians for pregnancy, pediatrics, cycle disorders, or sleep conditions. Do not rely on calendar math alone for contraception.