how to check H1B Maxout period?

My wife got H1B stamped in 2012 and she never traveled to US. Wanted to know how long this visa valid for? how can the maxout day will be calculated for her visa?

The visa itself will have validity period mentioned on in, just like the approved 797.

However, she will be eligible to apply for cap-exempt H-1 petition during 6 years from original approval date (of late USCIS seems to be going easy on the 6 year requirement and allowing it for even older petitions).

Once she enters US on H-1, she can stay for at most 6 years inside US on H-1 (only days spent inside US on H-1 and L-1 are counted).