Your Due Date
Cycle Information
Average cycle is 28 days. Cycles between 21-35 days are considered normal. This affects the estimated last period date and ovulation timing.
Conception Timeline
Last Menstrual Period
Thursday, January 8, 2026
Fertile Window Begins
Saturday, January 17, 2026
Ovulation / Estimated Conception
Thursday, January 22, 2026
Fertile Window Ends
Friday, January 23, 2026
Due Date
Thursday, October 15, 2026
Understanding the Results
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.
Key Dates Summary
| Event | Date | Notes |
|---|---|---|
| Last Period (LMP) | Jan 8, 2026 | Start of gestational age |
| Fertile Window Start | Jan 17, 2026 | 5 days before ovulation |
| Estimated Ovulation | Jan 22, 2026 | Peak fertility day |
| Likely Conception | Jan 22, 2026 | Within 24 hours of ovulation |
| Due Date | Oct 15, 2026 | 40 weeks from LMP |
Conception Estimate
Estimated Conception
Jan 22, 2026
Week 38 • Trimester 3
Conception Window
Jan 17, 2026 - Jan 23, 2026
6-day fertile window
Conception Timeline Scenarios
Explore how changes affect your results
Conception Information
Based on your results
Your Timeline
Based on your due date of Oct 15, 2026 and 28-day cycle, conception likely occurred around Jan 22, 2026. This is approximately 38 weeks ago.
Conception Window
The actual conception could have occurred anytime between Jan 17, 2026 and Jan 23, 2026 due to sperm survival and egg viability.
Dating Accuracy
Ultrasound dating in the first trimester is more accurate than calculations. If your provider adjusts your due date, the conception estimate would shift accordingly.
Frequently Asked Questions
How is conception date calculated?
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.
Why is there a conception range instead of exact date?
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.
What is the difference between conception date and gestational age?
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.
How accurate is the estimated conception date?
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.
Can I determine paternity from conception date?
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.
How this works
Formulas are implementations of published clinical or public-health equations. Calculations run in your browser — no inputs are transmitted to our servers and no account is required. The result is informational; it does not diagnose, treat, or replace advice from a clinician.
What this tool can’t do
When to consult a professional
Talk to a licensed healthcare provider before using the output of this tool to make a medical decision, especially if you have an underlying condition, are pregnant, or are on medication that affects metabolism or fluid balance.
Sources
- [1]Centers for Disease Control and Prevention (CDC)Official sourcecdc.govAccessed Apr 21, 2026
- [2]National Institutes of Health (NIH)Official sourcenih.govAccessed Apr 21, 2026
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