Ovulation or fertility kits help women know on which days they are most likely to become pregnant. If you’re planning a pregnancy, then you’ll want to know how these kits work. This free article should help.

We Know: How Fertility and Ovulation Kits Work

When am I most likely to become pregnant?

You are most likely to become pregnant on the day during your period when you ovulate and the day before. In fact, the five days preceding ovulation are sometimes called the fertility window, so pregnancy is likely any time during the five days, and particularly on the last two.

(Ovulation, by the way, is when the ripe egg leaves the follicle.)

How do Ovulation Kits know I'm ovulating?

A day or two before you ovulate, a lutenizing hormone (LH) is at peak production. Ovulation kits work by detecting the high level of this hormone in your blood or urine. Just how and when the hormone spikes differs in different women, but it’s a pretty good predictor of fertility.

How do I use the Ovulation Kit?

To use most home ovulation kits, you either urinate onto an absorbent stick, or dip a stick into a cup or urine or, place drops of urine onto a cassette. In each case, you look to see if the color in the measuring window changes. Kits come with multiple sticks, because you’ll probably need to check more than once. The kits cost from $10 to $40.

Some fertility kits come with a monitoring device. You put the stick with your urine sample into the device and it reads the sample for you. It measures more than just your LH level. These devices are very reliable and cost about $200.

If you want to read more about ovulation kit reliability, check with publications such as Consumer Reports.

Remember: These kits have varying levels of success and it is not a good idea to use a fertility kit as a reliable way to avoid pregnancy.