Chance of Pregnancy Calculator
Tick the days you had sex around ovulation to estimate the chance of a pregnancy this cycle, based on day-by-day rates measured in a large fertility study.
Medical disclaimer. This calculator is for general information and education only. It is not medical advice, not a diagnosis, and not a substitute for professional care. These are average rates for couples in one study, not your personal odds, which depend on age, health and both partners' fertility. Do not use this calculator to avoid pregnancy.Speak to a doctor or another qualified clinician about any health decision.Last reviewed .
Not sure when you ovulate? Try the ovulation calculator. Already past ovulation? The DPO calculator shows when a test is worth taking.
Where these numbers come from
The day-by-day rates come from Colombo and Masarotto (2000), an analysis of couples using natural family planning at European centres who recorded their temperature and every day they had sex. Among 3,175 cycles with sex around ovulation, there were 434 pregnancies. Day 0 is the study's ovulation marker, the shift in basal body temperature, which is usually within a day of true ovulation. A "pregnancy" here is one that lasted long enough to be detected.
To combine several days, the calculator uses the same statistical model the authors fitted, by Schwartz and colleagues (1980). It treats each day's chance as independent, and caps the total at the share of cycles able to produce a pregnancy, about 28% in this group. That is why ticking more days raises the estimate, but never past that ceiling. The authors note this model can slightly underestimate the chances for couples who have sex very often.
The pattern matches other research. A study of North Carolina women by Wilcox and colleagues (1995) found a six-day fertile window ending on the day of ovulation, with chances rising from about 10% five days before to 33% on the day itself. The exact figures differ between studies because of how ovulation was measured and who took part, so treat any single number as a rough guide rather than a prediction.
Frequently asked questions
What are the chances of getting pregnant on each day of the cycle?
In a European study of 3,175 cycles (Colombo and Masarotto, 2000), sex on a single day led to a pregnancy about 7% of the time five days before ovulation, 18% four days before, 24% three days before, 26% two days before, 21% the day before, and 10% on the day of ovulation. More than a few days outside that window, the chance was close to zero. The table on this page shows every day with its uncertainty range.
When is the best time to have sex to get pregnant?
In the days just before ovulation. The study behind this calculator found the four days before ovulation were the most fertile, peaking two days before. Sperm can survive for several days, while the egg lives for about a day, which is why sex before ovulation counts for more than sex after it. Having sex every one or two days through that window covers it without needing to pinpoint ovulation exactly.
Why is the highest chance only about 25–28%?
Even perfectly timed sex does not lead to a recognised pregnancy every time. In the statistical model used here, about 28% of cycles in this group of couples were capable of producing a pregnancy at all (the "cycle viability"), so that is the ceiling no matter how often you have sex. Over several cycles the chances add up: most couples in studies like this conceive within a year.
Does age change the chances?
Yes, on average fertility declines with age, especially from the mid-30s. This particular study did not find a clear difference between its age groups, but a later analysis of the same couples by Dunson and colleagues (2002) estimated that day-specific chances for women aged 35 to 39 were about half those for women aged 19 to 26, and also lower when the male partner was over 35. The numbers here are averages for a group whose women were about 29 on average.
Can I use this to avoid pregnancy?
No. A calculator cannot reliably tell you when you are not fertile: ovulation dates are estimates, cycles vary, and the study still estimated a small chance from sex as early as eight days before its ovulation marker. If you want to avoid pregnancy, use a reliable method of contraception and speak to a clinician about the options.