If you allow too much tax to be withheld, you get a refund. You can determine how much is tax is taken out of your pay by the number of allowances you claim on your W-4. The W-4 has a worksheet to help you figure out how many personal allowances to take.
Step 5: Predict your next period. Now that we know how long your period cycle is, we can just use it to count the days to predict your next period. My period cycle is 28 days so if I count 28 days from February 10, that's when my next period should come.
It is a good alternative way to determine your ovulation though, if your periods are irregular. Use an ovulation prediction kit. You can also get a ovulation prediction kit over the counter at any drugstore for a good price, and you can use it to track your ovulation as well.