Free Tools
Fertility Calculator Suite
Clinical-grade tools used by IVF clinics — free to use, free to join. Create a free account to see your results.
These tools are for informational purposes only and are not a substitute for medical advice. Always consult your GP, midwife, or fertility specialist for clinical decisions.
Ovulation & Fertile Window Calculator
Find your most fertile days. Uses the luteal phase model validated by Wilcox et al. (NEJM, 2000).
days
Typical range: 21–45 days. 28 is average.
days
Usually 12–16 days. Leave at 14 if unsure.
When to see your GP
If you're under 35 and have been trying for 12 months, or over 35 and trying for 6 months, ask for an NHS fertility referral. Testing is free on the NHS.
Tracking your cycles
For the most accurate ovulation prediction, track 3–6 cycles. Ovulation predictor kits (OPKs) detect the LH surge 24–48 hours before ovulation.
HCG in early pregnancy
HCG levels vary widely between individuals. A single value matters less than the rate of rise. Always discuss results with your healthcare provider.