According to a report by Mehr News Agency, quoting latest data from Iran's national oil company

US sanctions are to hit Iran in two parts, one in August and the harshest sanctions to kick into effect in November. The 500k bpd fall here isn't as bad as feared, as the market was gauging something between 500k to 2 mil bpd as a result of the sanctions imposed.

It will be highly dependent on which countries are willing to listen to the US and abide by these sanctions and not deal with Iran. The US will likely not encounter problems in getting Japan to conform, but the real issue will be getting India and China to follow suit.