Calculate your estimated conception date based on your due date. Find out when conception likely occurred and understand your fertile window.
Estimated Conception
Jun 22, 2025
Week 36 • Trimester 3
Conception Window
Jun 17, 2025 - Jun 23, 2025
6-day fertile window
Average cycle is 28 days. Cycles between 21-35 days are considered normal. This affects the estimated last period date and ovulation timing.
Last Menstrual Period
Sunday, June 8, 2025
Fertile Window Begins
Tuesday, June 17, 2025
Ovulation / Estimated Conception
Sunday, June 22, 2025
Fertile Window Ends
Monday, June 23, 2025
Due Date
Sunday, March 15, 2026
Conception Window: The 6-day period when conception was most likely. This accounts for sperm survival (up to 5 days) and egg viability (24 hours).
Accuracy: These dates are estimates based on average cycles. Actual conception may vary by several days, especially with irregular cycles.
Medical Dating: Your healthcare provider may adjust dates based on early ultrasound measurements, which can be more accurate than calculations.
| Event | Date | Notes |
|---|---|---|
| Last Period (LMP) | Jun 8, 2025 | Start of gestational age |
| Fertile Window Start | Jun 17, 2025 | 5 days before ovulation |
| Estimated Ovulation | Jun 22, 2025 | Peak fertility day |
| Likely Conception | Jun 22, 2025 | Within 24 hours of ovulation |
| Due Date | Mar 15, 2026 | 40 weeks from LMP |
Estimated Conception
Jun 22, 2025
Week 36 • Trimester 3
Conception Window
Jun 17, 2025 - Jun 23, 2025
6-day fertile window
Explore how changes affect your results
Based on your results
Based on your due date of Mar 15, 2026 and 28-day cycle, conception likely occurred around Jun 22, 2025. This is approximately 36 weeks ago.
The actual conception could have occurred anytime between Jun 17, 2025 and Jun 23, 2025 due to sperm survival and egg viability.
Ultrasound dating in the first trimester is more accurate than calculations. If your provider adjusts your due date, the conception estimate would shift accordingly.
Conception typically occurs about 2 weeks after the first day of your last period (around ovulation). From due date, conception = due date minus 266 days. From LMP, conception ≈ LMP + 14 days.
Conception typically occurs during ovulation, about 14 days before the next period. From due date, we subtract 266 days (38 weeks). Since sperm can live 5 days and the egg 24 hours, the actual conception window spans several days.
Sperm can survive in the reproductive tract for up to 5 days, and the egg is viable for about 24 hours after ovulation. Intercourse anywhere in this 6-day window can result in conception, making the exact date uncertain.
Gestational age starts from the first day of your last menstrual period (LMP), about 2 weeks before conception. So at "2 weeks pregnant" conception hasn't occurred yet. Fetal age is actual time since conception, about 2 weeks less than gestational age.
Accuracy depends on cycle regularity. For regular 28-day cycles, accuracy is within a few days. Irregular cycles, stress, or late/early ovulation can shift actual conception. Ultrasound dating in the first trimester is most accurate.
The conception date range can help narrow down when conception occurred, but is not definitive proof of paternity. Given the 6-day fertile window and variation in cycle timing, DNA testing is the only certain way to determine paternity.
Estimated Conception
Jun 22, 2025
Week 36 • Trimester 3
Conception Window
Jun 17, 2025 - Jun 23, 2025
6-day fertile window