Free · Gynecology & pregnancy calculators 🤰

Pregnancies per 100 Woman-Years of Equal Follow-Up

This equal-follow-up model treats every participant as exposed for the entered number of months.

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Calculator inputs

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How to use this calculator

  1. Enter the known values in the units shown. Results update as you type.
  2. Where results are editable, change one to solve backwards. Lock a value to hold it fixed.
  3. Use the worked example to check the method. Reset restores the starting fields.

Use the result with context

Health results are educational estimates, not a diagnosis or treatment recommendation. A qualified clinician can interpret measurements in the context of your health.

Formula and method

Two pregnancies among 100 participants each followed for 12 months give 2 pregnancies per 100 woman-years.

Pearl index = 1200 × pregnancies / (women × months of equal exposure).

Worked example

Enter these known values and leave the other values blank.

Participants with equal follow-up
100 #
Exposure duration per participant
12 mos
Participants with a pregnancy
2 #
Pregnancies per 100 woman-years
2

Assumptions and limitations

  • This equal-follow-up model treats every participant as exposed for the entered number of months. Trials with different follow-up need summed person-time instead. Pregnancies, not infants, are counted; the result is a rate, not a pregnancy probability. Comparative contraceptive failure percentages require study-specific evidence.
  • Clear an unknown control before solving the supported arithmetic relationship.
  • This model does not select medical treatment or establish a diagnosis.

Common questions

How is the result calculated?

Pearl index = 1200 × pregnancies / (women × months of equal exposure).

When does this model apply?

This equal-follow-up model treats every participant as exposed for the entered number of months. Trials with different follow-up need summed person-time instead. Pregnancies, not infants, are counted; the result is a rate, not a pregnancy probability. Comparative contraceptive failure percentages require study-specific evidence.

References

Bookify adds independently reviewed bounds: isInteger(allWomen) and allWomen > 0; isInteger(pregnantWomen) and pregnantWomen >= 0; months > 0.

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