Is there any limitation on how many days in a year one can stay on a visitors visa

[OnePartPoker]

Quick question, friends. 

For parents visiting on tourist visa, is there any limitation on how many days they can stay here *in a year* ? Calendar or otherwise.

I know they can stay for the validity of the visa issued at port entry, which is usually 6 months, but my question is more about max they can stay in a year. 

For instance, if they stay in the US for 6 months, can they go to India and come back in the same year?

Any experiences you can share are much appreciated 🙏

[JoeF]

It is never about the calendar year. People should stay aroad more than in the US on visitor visa to avoid the appearance of living in the US. After 6 months in the US a visitor should be more than 6 months outside the US.