Estimate your chance of pregnancy from a single encounter using the pull-out (withdrawal) method. This simple calculator uses cycle timing and whether use was typical vs perfect.
Methodology & limits
What this estimates
This tool estimates the chance of pregnancy from a single act of intercourse when using withdrawal. It adjusts for cycle timing on the selected date and optional personal factors. Results are expressed as a per-act percentage and an “about 1 in N” figure.
Model overview
The backend model provides an average per-act conception probability for a random day in the cycle based on female age. We then adjust that average to the exact day you select using a fertile-window weighting. Optional modifiers for male age, BMI, work hours, cigarettes, and alcohol apply as odds-ratio multipliers to the baseline. If you add up to two more contraceptive methods, those methods are passed to the server and combined there. We do not combine method failure rates in the browser.
Timing and fertile-window adjustment
You enter the intercourse date, the start date of your last period, and your typical cycle length. We identify the high-fertility day and reweight the baseline per-act probability across the cycle with a six-day fertile window and very low weights outside it. This aligns with evidence that the chance of conception is concentrated from about five days before ovulation through ovulation day, peaking near the day before ovulation. For irregular or unknown cycles, a 28-day length is used by default.
Withdrawal as the primary method
Withdrawal is treated as the primary contraceptive. You can choose typical use or perfect use. Typical use includes real-world lapses and the small risk related to pre-ejaculate, while perfect use represents consistent timing and complete withdrawal before ejaculation. The calculator reflects these differences via method-specific effects in the backend model.
Additional methods
You may add up to two more methods from the list. Duplicate labels are de-duplicated and only the first three unique methods are sent. Methods are combined on the server relative to an anchor intercourse frequency and annual baseline, then returned as a single per-act probability for this calculation.
Age and lifestyle modifiers
Female age drives the baseline fecundability. Male age and lifestyle inputs adjust the odds up or down with modest multipliers based on published associations. If you leave these fields blank, sensible defaults are applied.
Display rules
Because very small probabilities can look like 0, values under 0.0001% are shown as “< 0.0001%.” Extremely high day-specific results are capped visually to avoid misleading spikes. The “about 1 in N” line is included for easier interpretation at low probabilities.
Assumptions and limits
This is an estimate, not a diagnosis. It assumes one act on the selected date, sperm and egg are otherwise healthy, and cycles are ovulatory. It does not directly capture where ejaculation occurred or the use and timing of emergency contraception. If ejaculation occurred inside the vagina or withdrawal was late, risk is likely higher than shown. If you are considering emergency contraception, it is more effective the sooner it is taken. For personalised advice, speak with a clinician.
Sources
Key inputs and structure draw on: studies of day-specific fertility across the menstrual cycle; method effectiveness summaries from Contraceptive Technology and peer-reviewed analyses of typical versus perfect use; and epidemiologic work on age and lifestyle factors and fecundability. Representative references include Wilcox et al., NEJM 1995 and 1998 on the fertile window; Trussell and colleagues on contraceptive failure by use quality; and Hatcher et al., Contraceptive Technology (latest ed.).
Medical disclaimer
Information here is for education only and is not medical advice. If you have concerns about pregnancy risk or emergency contraception, consult a healthcare professional.
This simple estimator uses published typical vs perfect failure rates for withdrawal and adjusts for cycle timing (higher risk near ovulation, lower risk far from it). It does not account for:
- multiple rounds in one day
- where ejaculation occurred (inside/outside/on)
- emergency contraception (EC) taken after the encounter
If any of the above apply, see the “What’s next?” options below for tools that better fit your situation.
Educational tool only; not medical advice.
Good to know
- Typical vs perfect use matters. If withdrawal was late or there were slip-ups, choose typical use for a more realistic estimate.
- Repeat rounds increase risk. Residual sperm can carry into pre-ejaculate during later encounters the same day.
- Only condoms help with STIs. Withdrawal does not reduce STI risk.
Withdrawal FAQ
Does this calculator handle multiple rounds?
No. It assumes a single encounter. For repeat rounds or more nuance, use the Advanced Pregnancy Chance Calculator.
Where ejaculation happened — does that change the result?
This page’s estimator doesn’t take that input. If ejaculation occurred inside the vagina, risk is higher than withdrawal; consider the EC Effectiveness tool and the Daily Chance Calendar.
Does it include emergency contraception?
Not here. Use the dedicated Morning-After Pill Effectiveness Calculator to see expected impact by timing and pill type.