A snap general election this autumn would need to follow a strict timetable specified in law.
Parliament has to be dissolved 25 working days before polling day.
If he picked Thursday October 24 for polling day, dissolution would need to take place on September 19.
October 17 would require dissolution on September 12, and October 10 would mean dissolution on September 5.
Before dissolution, however, MPs have to debate and vote on a motion to hold a general election.
The motion would pass only if two-thirds of the total number of seats in the Commons (currently 434 out of 650 MPs) vote in favour.
In 2017, there was a gap of two weeks between MPs voting to hold a snap election and the date of dissolution.
Events would need to move at a much faster pace this time, with MPs only returning from their summer recess on September 3 - two days before the date of dissolution needed for an October 10 election.
These scenarios presume that polling day has to be on a Thursday, as it has been for every general election since 1935.
In theory polling day could take place on any day of the week - though timings would still be tight for it to happen before October 31.
The last time the UK held a general election in the month of October was 1974.
Further back, the last time a general election took place in November was 1935, while there has not been one in December since 1923.
Strict rules also dictate the sequence of events were the Government to lose a vote of no-confidence.
If a majority of MPs vote to say they do not have confidence in Boris Johnson’s Government, a 14-day period is automatically triggered beginning at midnight on the same day.
During these 14 days, MPs have the chance to form a new government that can win a vote of confidence.
If MPs were to fail to pass a motion of confidence in a new government by the end of this period, a general election would be automatically triggered.
There would then need to be a further 25 days between the dissolution of Parliament and polling day.
The actual date of the election would be picked by Boris Johnson.
He might decide to choose a date beyond October 31, after the UK is due to leave the EU, possibly without a deal.
On the other hand Mr Johnson might respond to a vote of no confidence by calling an election immediately.
Either way, the 25-day period between dissolution and polling day applies.