How to calculate bonus for a year?

You really have to be kidding. How do you expect us to answer that question?

The amount of a bonus is dependent on the company rules for providing a bonus. A bonus may simply be a percentage of salary. But it may be based on a formula based on merit or it may be based on company performance. There could be a number of rules tied to how the bonus is calculated.

In the future, please think your question through before posting and provide us with enough information to attempt to answer.