Conception Calculator
Adjust the inputs below. Results update as you type.
How it works
Ovulation typically occurs 14 days before the next period. For a 28-day cycle, add 14 days to LMP to estimate ovulation/conception. Fertilization occurs within 12–24 hours of ovulation; sperm can survive 3–5 days. Cycle length variability means conception windows shift—this is an estimate, not a clinical determination. Confirm dates with an OB/GYN.
Input guidance
- Use measured values (recent weight, height, activity level) rather than guesses.
- Recalculate every few weeks as your routine and body metrics change.
- Pair screening metrics with context such as sleep, stress, and medical history.
The formula
Conception is estimated around ovulation, about 14 days before the next expected period, or roughly 266 days before the due date.
Worked example
On a 28-day cycle starting June 1, ovulation and likely conception fall around June 14–15.
More examples to test
- Maintenance case: keep activity constant and observe expected baseline ranges.
- Adjustment case: change only one major variable to understand sensitivity.
How to interpret results
Use results for awareness and planning, then validate with qualified medical or nutrition professionals for individualized decisions.
When this can be inaccurate
Population formulas cannot account for all biological factors such as medical conditions, medication effects, body composition differences, and genetics.
Change history
- July 2026: Quality-reviewed for publication with formula checks and explanatory copy updates.
Site-wide corrections also appear on the corrections log.
Track fitness goals with a top app
General wellness resource.
Frequently asked questions
How is conception timing estimated?+
From your cycle: ovulation is about midway, and conception occurs near it. Sperm survival means the exact day can vary by several days.
Can it pinpoint the father's timing?+
Not precisely. Because sperm survive up to about five days, conception may not align with a single act of intercourse.
Is ultrasound more accurate?+
Early ultrasound dating is generally more reliable than calendar estimates, especially with irregular cycles.
Can this calculator diagnose a condition?+
No. It is a screening and education tool only, not a clinical diagnosis.
When should I seek professional advice?+
Seek professional advice when results are extreme, persistent, or conflict with symptoms, goals, or prior medical guidance.