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Chance of Pregnancy Calculator (by Day of Intercourse)

Estimate the chance of getting pregnant from intercourse on a given day of your cycle, based on your estimated ovulation date and the classic Wilcox day-specific conception probabilities.

First day of your last period

Average cycle length

Date of unprotected intercourse

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How it works

Ovulation ≈ first day of period + (cycle length − 14) days · chance = Wilcox day-specific probability: day −5 10%, −4 16%, −3 14%, −2 27%, −1 31%, ovulation day 33%, day +1 ≈ 0%

Wilcox and colleagues followed 221 couples trying to conceive and measured ovulation with daily urine hormones (NEJM 1995). Every pregnancy came from intercourse in a six-day window ending on the day of ovulation; the chance from a single act rose from about 10% five days before ovulation to about 31–33% on the day before and the day of ovulation, and was essentially zero afterwards. Because sperm survive up to five days but the egg only about a day, the best days are the 2–3 days before ovulation. This calculator estimates ovulation as 14 days before your next expected period, which can be off by several days in real cycles.

Worked example

Your last period started on September 1, 2026 and your cycles last 28 days, so ovulation is estimated on September 15, 2026 (cycle day 15). Intercourse on September 14, 2026 (cycle day 14) is 1 day before ovulation, which gives about a 31% chance of pregnancy — inside the fertile window of September 10–15, 2026.

Sources: Wilcox AJ, Weinberg CR, Baird DD (1995) Timing of sexual intercourse in relation to ovulation. N Engl J Med 333:1517–1521 · ACOG — Fertility awareness-based methods of family planning

Frequently asked questions

What day of my cycle am I most likely to get pregnant?

The highest chances come from intercourse 1–2 days before ovulation and on the day of ovulation itself — about 27–33% per act in the Wilcox study. In a 28-day cycle that is roughly cycle days 12 to 15.

Can I get pregnant right after my period?

It is possible if you have short cycles, because sperm can survive up to 5 days. With a 21–24 day cycle, ovulation can happen around day 7–10, so intercourse just after bleeding can fall inside the fertile window.

Can I get pregnant after ovulation?

Very unlikely. The egg survives about 12–24 hours, so the chance one day after ovulation was estimated at zero (with an upper limit of about 12%). Your ovulation date is only an estimate, though, so the real fertile window may be shifted.

How accurate is this calculator?

It uses average probabilities and an estimated ovulation day. Real ovulation varies from cycle to cycle, so ovulation tests, cervical mucus or basal body temperature give a better picture. It must not be used as birth control.

Related calculators

Ovulation Calculator

Find your estimated ovulation day, fertile window, peak days and next period from your last period and cycle length — with a luteal-phase setting, irregular-cycle range and a table of your next six cycles.

Fertile Window Calculator

Find your fertile window, most fertile days and estimated ovulation date from your last period, cycle length and luteal phase, with the day-by-day chance of conception (Wilcox study), an irregular-cycle range and your next six cycles.

DPO Calculator

Count how many days past ovulation (DPO) you are on any date, with your implantation window, the earliest day a sensitive pregnancy test may turn positive and when your period is due.

When to Take a Pregnancy Test Calculator

Find the earliest sensible day to test and the day results are reliable, from your ovulation date or last period.

Basal Body Temperature Calculator

Enter 6 low basal temperatures and the next 3 readings to draw your BBT coverline and check the 3-over-6 rule that confirms ovulation has happened, in °C or °F.

This calculator gives population averages for education only. It is not a method of contraception or a diagnosis — talk to your doctor, gynecologist or fertility specialist about your own situation.