Before you can be sure when to start testing, you need to work out your usual cycle length. The length of your cycle is the number of days from the day your period starts (Day 1) to the day before your next period starts.
The length of the cycle can vary from one woman to another, and can vary from cycle to cycle in the same woman.
To make sure that the hormone level in your urine is concentrated enough for the test to detect, it’s important not to urinate for at least 4 hours before doing the test.
You can test at any time of the day, but it should be at the same time each day. Many women find that first thing in the morning is the most convenient.