The UK could be offered a Brexit delay to 22 May on the condition MPs approve the PM's deal next week, a draft European Council document says.
EU leaders are still in discussions in Brussels over the UK's request to postpone the 29 March exit date by three months.
However there have been reports that an extension could be offered until 7 May only.
The draft document says no extension is possible beyond the European elections.
In Brussels, Prime Minister Theresa May spoke to leaders to try to get their backing for a delay, after MPs twice rejected the withdrawal deal she has negotiated with the European Union.
She has told European Council President Donald Tusk that she needs more time to get her deal agreed by MPs and passed into law.
The BBC's Brussels correspondent Adam Fleming said Mrs May had spoken to EU leaders for 90 minutes and was asked several times what her contingency plans were if she lost the third "meaningful vote" on her deal in Parliament.