Estimate conception timing and the fertile window from your last period and cycle.
Understanding the pregnancy conception calculation
Enter your last period and cycle length to estimate ovulation and the fertile window when conception is most likely. It’s a general estimate, not a medical tool.
A worked example
The calculator opens with a cycle length of 28. On those figures the estimated ovulation is Aug 15. Underneath, Fertile window comes out at Aug 10 – Aug 16 and Next period at Aug 29. Change any field and every figure updates as you type.
How to fill it in
- Enter your figures in the fields provided.
- The result updates as you type.
- Review the breakdown below the main number.
The formula
ovulation ≈ last period + (cycle length − 14) days
Common questions
How is conception timing estimated?
From ovulation, about 14 days before the next period, plus the days around it.
Can I rely on this?
Use it as a guide; actual timing varies between cycles.