Enter the pill type, the timing of the missed dose and intercourse, and any emergency contraception to see an estimated pregnancy chance, a broad model range, next-step guidance, and a pregnancy-test date.
What Increases Pregnancy Risk After Missing the Pill?
The calculator raises its estimate when one or more of these apply:
- An active pill was missed. A missed placebo or reminder pill does not raise the estimate if the next active pack starts on time.
- More pills were missed or the dose was later. The relevant window depends on the pill: more than 3 hours for norethindrone or norgestrel POPs, more than 12 hours for desogestrel, and 48 hours or more—usually two consecutive missed pills—for combined or drospirenone pills.
- The lapse extended the hormone-free interval. This includes some week 1 lapses and combined-pill week 3 lapses when the placebo interval is not skipped.
- Earlier active pills were not taken correctly, or active pills were not restarted. This can lengthen the concern window.
- Intercourse occurred inside the concern window. Depending on the pill and pack position, this can include days before the missed pill and continue until protection is restored. More intercourse dates inside that window can raise the episode estimate.
- Emergency contraception was not used promptly. The method and time since intercourse affect the estimate. Restarting hormonal pills within 5 days after ulipristal may reduce its expected benefit.
- The model uses a higher age-based starting chance. Age changes the baseline applied before the missed-pill and emergency-contraception adjustments.
Vomiting, severe diarrhea, enzyme-inducing medicines, St John’s wort, body weight effects on oral emergency contraception, and ovulation timing can also matter, but this calculator does not quantify them. Ask a pharmacist or clinician if any applies.
If the pill formulation or event times are unknown, the calculator uses a more conservative path and a wider range. That uncertainty does not by itself mean pregnancy is more likely.
Methodology
How accurate is this calculator?
The percentage is an estimate, not a measured personal probability. Clinical guidance can identify whether pill protection is expected to remain in place and what action to take, but studies have not measured a pregnancy rate for every combination of missed pills, pack position, intercourse timing and emergency contraception.
The result therefore shows a central modeled percentage and a broad approximate range. The range is a sensitivity range, not a statistical confidence interval. The result becomes more useful when the pill formulation and event dates are known, but it cannot determine ovulation or guarantee an outcome.
How the estimate is calculated
The model starts with an age-scaled, cycle-average chance from one act without contraception. It then applies a very-low protected floor and moves toward the unprotected baseline only when the entered scenario crosses the relevant missed-dose threshold. Missing a placebo pill does not add risk. One combined active pill under 48 hours and one drospirenone pill under 48 hours remain on the protected path.
The concern window is selected from the pill rules rather than always beginning before the lapse. CDC combined-pill and drospirenone guidance can include the preceding five days when two or more active pills are missed in week 1. The model also uses that five-day lookback for a confirmed extended hormone-free interval as a conservative planning assumption. Traditional POP and specialist desogestrel guidance begin the window when the first pill is missed. For desogestrel 75 microgram pills, current specialist guidance uses 48 hours after correct pill-taking restarts, while current licensed pill leaflets commonly use 7 days and can warn about intercourse in the preceding week when seven correct pills were not established. When the instructions are unknown, the central estimate uses the longer path and the model range includes both. Emergency contraception is applied act by act from the entered intercourse and EC times. It is never timed from the day the page is viewed, and it is not applied to intercourse after EC.
For multiple dates, the model uses a bounded episode calculation rather than treating every act as a completely separate pregnancy opportunity. The testing date is 21 days after the latest entered intercourse date when period timing is unknown.
Clinical guidance and evidence
- CDC: combined hormonal contraceptives
- CDC: progestin-only pills
- FSRH/CoSRH: progestogen-only pills, including desogestrel missed-pill guidance
- Licensed desogestrel 75 microgram patient leaflet
- CDC: emergency contraception
- Wilcox et al.: intercourse timing and conception probability
- Glasier et al.: ulipristal and levonorgestrel emergency contraception
- Cleland et al.: copper-IUD emergency contraception
- NHS: pregnancy-test timing
The clinical branches come from published guidance. The percentage conversion and broad model range are Pregnancy Chance Calculator estimates, not measured personal probabilities.