Release Predict your GF's period with Periodic Calendar!

[ekianjo]

According to Wikipedia, the reliability of the pill is 99.7% if used correctly, 92% with typical use (in which people sometimes forget to take a pill). The reliability of calender methods is 91 to 95% if used correctly, 88% with typical use.

There is quite a big difference between 0.3% and 5%.

It does not really matter at that stage, the fact that the risk is there makes is an issue in both cases.