Missed Period & Pregnancy Probability Calculator
Assess pregnancy likelihood based on your menstrual cycle and intercourse dates. Visualizes your specific fertile window and conception overlap probability.
About
A missed period is often the first sign of pregnancy but anxiety can delay menstruation creating a confusing cycle. Understanding the biological timing of conception helps clarify the situation. Pregnancy is only possible if intercourse occurred during the "Fertile Window" a specific phase surrounding ovulation when an egg is viable.
This tool maps your cycle to pinpoint Ovulation (roughly 14 days before the next expected period) and calculates the overlap between sperm viability (up to 5 days) and the egg's lifespan (12 to 24 hours). By comparing your intercourse date with this window we generate a probability score helping you decide if a test is necessary.
Formulas
The calculator estimates the Fertile Window relative to the Next Period Date:
If the intercourse date falls within Windowstart and Windowend the probability is flagged as High or Medium.
Reference Data
| Event | Timing (28-day cycle) | Conception Chance |
|---|---|---|
| Menstruation | Day 1 - 5 | Near Zero |
| Follicular Phase | Day 6 - 9 | Very Low |
| Fertile Window Start | Day 10 - 12 | Medium (Sperm survives) |
| Ovulation Peak | Day 13 - 14 | High |
| Post-Ovulation | Day 15 - 16 | Low (Egg dying) |
| Luteal Phase | Day 17 - 28 | Zero |