When did the US Immigration Service start calculating?

There is no actual immigration supervision in the United States.

In fact, American immigration law does not recommend that green card holders enter the country once every six months. But why does everyone tend to do this? What is the legal basis?

According to the immigration law, if the green card holder stays in a country outside the United States for less than half a year at a time, if the immigration officer thinks that you don't need to live in the United States for a long time and wants to take back your green card, he will prove that you have the intention to give up your green card. It's very troublesome for him.

If you have stayed overseas for more than 6 months and less than 1 year, then when the immigration officer thinks that you don't need to live in the United States for a long time and wants to cancel your green card, you have the responsibility to obtain evidence to prove that you have no intention of giving up your green card.

"Immigration supervision" is a vivid metaphor. For example, if you want to immigrate to a country, you can't leave the country for a long time (short time) like a prison, because if you leave the country for a long time, you can't apply for naturalization or lose your immigration status.

Simply put, you have an American green card. It is best to land in the United States every 180 days, regardless of time, even if you leave the country in 3-5 days. If you live in the United States for more than two and a half years within five years, you can apply for American citizenship, which means canceling immigration supervision.

If immigrants need help, they can go to Baidu American Direct Investment Immigration Service Center.