❤️

Contraception Effectiveness Calculator

Compare typical-use and perfect-use failure rates of contraceptive methods and see the cumulative chance of pregnancy over several years.

Method

Use

Over how many years

Loading calculator…

How it works

Failure rate = pregnancies per 100 women in the first year (typical vs perfect use) · Effectiveness = 100 − failure rate · Cumulative over N years = [1 − (1 − p)^N] × 100, where p = failure rate ÷ 100

Contraceptive effectiveness is quoted two ways. Perfect use assumes the method is used correctly and consistently every time; typical use reflects real life, including missed pills and inconsistent condoms. The gap is largest for user-dependent methods: the pill is over 99% effective in perfect use but around 91% in typical use, while implants and IUDs are nearly identical either way because there is little to get wrong. Small annual failure rates also compound — a 9% yearly rate becomes a much larger chance across several years.

Worked example

The combined pill has a 9% typical-use first-year failure rate, so about 91% effectiveness. Over 3 years the cumulative chance of pregnancy is [1 − (1 − 0.09)^3] × 100 ≈ 25%, showing how small annual rates add up.

Sources: CDC — Contraceptive effectiveness

Frequently asked questions

Why is there such a big gap for the pill and condoms?

These depend on the user doing something correctly every time. Missed pills or inconsistent condom use push the typical-use failure rate well above the perfect-use figure. Long-acting methods like implants and IUDs remove that human variable.

What do these percentages actually mean?

They are the number of women out of 100 who become pregnant in the first year of use. A 9% rate means about 9 of 100 pill users conceive within a year in typical use.

Do any of these protect against STIs?

Only condoms reduce the risk of sexually transmitted infections. Hormonal methods, IUDs and fertility awareness do not, so condoms are often used alongside them.

Related calculators

Menstrual Cycle Phase Calculator

Find which phase of your cycle you are in today — menstrual, follicular, ovulatory or luteal — from your cycle length and the day of your cycle.

Fertility Window by Cycle Length

See which days of your cycle are fertile from your average cycle length alone — as cycle-day numbers, no dates needed.

Menstrual Cycle Calculator

Map your menstrual cycle — period, follicular phase, fertile window, ovulation, luteal phase and likely PMS days — with today’s cycle day and phase, a luteal-phase setting and dates for your next six cycles.

PMS Symptom Window Calculator

Estimate the days each cycle when PMS symptoms are most likely — the late-luteal window before your next period — from your last period date and cycle length.

Educational estimate only, not medical advice. Cycles, nutrient needs and risk vary between people — discuss decisions with a qualified clinician.