Front-runner Boris Johnson appears almost certain to make it on to the final ballot, which will go to Tory members who decide the next occupant of Number 10.
Two more rounds of voting will decide whether Jeremy Hunt, Michael Gove or Sajid Javid will face him.
Thursday June 20
The fourth ballot will see Tory MPs eliminate another candidate, leaving just three contenders.
Voting will take place in a Commons committee room between 10am and noon, with the result announced around 1pm.
The final round of voting will take place between 3.30pm and 5.30pm, with the result announced around 6pm.
Saturday June 22
The first hustings for members, organised by Conservative Campaign Headquarters, will take place in Birmingham.
The party aims to hold hustings in all 12 regions of the UK to allow Tory members to see the candidates in action, and there will also be an opportunity for the public to question them online.
Both the BBC and Sky have said they will invite the final two candidates to take part in special TV programmes.
Conservative members should receive their postal ballots.
Week commencing July 15
The final hustings will take place in London.
Week commencing July 22
A new leader will be announced following the ballot of 160,000 Conservative members.
Prime Minister Theresa May will then see the Queen to formally resign and the new leader will be invited to Buckingham Palace to form a government.