Anytime during the month.

The only possible way you can find out is via a very sensitve and accurate thermometer and long term charting looking for temprature chages. And you will see a monthly pattern.

Otherwise literally you can ovulate at any time of the month. You can not use your Period as a reference to find exactly when.

General guide is that you will likely ovulate about 12-16 days before the next period is due regardless of how long your cycle is. If your cycles are irregular, this would be altered.

However, that is only a starting place and, as smoothy said, it can vary. While many women will follow this type of pattern, others will naturally ovulate a bit sooner or a bit later and even a day can make the difference between becoming pregnant or not. You can also, on occasion, ovulate outside of what is the norm for you. This is why there is no 100% safe time to not become pregnant, only times that are either more or less safe. The same would hold true when trying to become pregnant... some times are more likely than others.

Many women will notice changes prior to ovulation, especially an increase in more fluid and clear discharge. This is designed to allow the sperm to survive for a few days waiting for ovulation to occur.

There are several means of getting a better idea of when your body is preparing for ovulation. The basal temping and charting, and ovulation predictor kits are two of the more common methods.