Contraceptive efficacy is generally assessed by measuring the number of unplanned pregnancies during use of a contraceptive method. Best index for measuring contraceptive efficacy is:

The two methods that are used to measure contraceptive efficacy are the Pearl index and Life-table analysis. The Pearl index is usually based on a lengthy exposure (usually 1 year) and, therefore, fails to accurately compare methods at various durations of exposure. This limitation is overcome by using the method of Life-table analysis. Life-table analysis calculates a failure rate for each month of use. A cumulative failure rate can then compare methods for any specific length of exposure. Ref: Park's Textbook of Preventive and Social medicine, 19th edition, Page 406.