When is it possible to apply for U.S. citizenship?

There are a number of requirements to apply for U.S. citizenship. The applicant must have been a lawful permanent resident (the two-year conditional period counts) for at least five years, must have good moral character, must not have any absences of more than six months, must have resided in the U.S. and been physically present for at least 2.5 years during the past five years, must be able to speak, read, and write English (with certain age exceptions), and must pass a test of U.S. history and civics.

Usually, about 2 year after receiving your permanent Green Card.

It would be a total of 5 years after the conditional green card is issued, but only after the conditions are removed.

There are different factors and qualifications; providing that you meet all the requirements, generally you must be a permanent resident for 5 years, this does include the 2 year conditional period.

After one receives the conditional green card, we start counting the years. The prospective candidate would be eligible for citizenship five years following the date he obtains the conditional green card as long as they spend more than half of that period in the US.

You can apply for U.S. citizenship when you have your green card. In order to be eligible to apply for U.S. citizenship, you have to live in U.S. at least 30 months out of the 5 years.