Brexit vote: June 23
There is just one thing stopping the date from happening - Prime Minister David Cameron's attempts to renegotiate Britain's relationship with the EU. Cameron has four demands that he wants every leader of an EU country to agree to before he calls a referendum and time really is running out if he wants to accomplish that and have the vote in June.
Cameron basically needs to get an agreement when the European Council meet on February 18. If he doesn't, Britain's electoral commission's recommendations, which require a certain amount of time between calling a referendum and holding a vote, pretty much make it impossible to hold the vote on June 23.
If the referendum isn't held in in June, the only other time it can really be held this year is September. July and August are bad dates to hold a vote because people are on their summer holidays and any time later than September it will get dark too early - early darkness means less people turn out to vote.
The government will not want to have the referendum in 2017. It would clash with national elections in France and Germany and will be halfway through the Conservative government's term in office - a time when voters can often take out their frustration at government failure at the ballot box.
Not everyone will be happy with the June 23 date though. It would mean that the referendum campaign would clash with the Scottish, Welsh, English council, and London Mayoral elections. Scottish National Party leader Nicola Sturgeon told the BBC's Andrew Marr show on Sunday that having the referendum "in parallel" with these other elections "would be disrespectful" to them.