LP is the days from ovulation to the last day of your cycle. It averages 14 days so if you have a 28 day cycle, you should ovulate around day 14 and have a 14 day LP. But I believe anything from 12-18 days is considered normal for LP, so ovulation may occur anywhere from CD10 to CD16.
Do you track your cycle at all? Charting your BBT (basal body temperature, if you're not familiar with the term) is very accurate for pinpointing ovulation, but it can only confirm rather than predict ovulation. Lots of women use ovulation tests (OPKs) which should be positive 24-48 hours prior to ovulation. They detect a surge in hormones which is quite short lived, so it can be easy to miss it so it's possible can ovulate even without a positive test. There's also charting symptoms, cervical mucus, etc which when everything is put together (I use Fertility Friend to keep track of everything) will form a very accurate picture of your cycle.
There's lots of resources online, but the best book I've ever read on the subject is Taking Charge of your Fertility if you're interested in finding out more.