Boris Johnson and Jeremy Corbyn are focusing on Brexit and public services in their final hours of campaigning.
In their last interviews with the BBC ahead of Thursday's poll, Mr Johnson repeated his main pledges, saying: "Only if you get Brexit done [can you] move the country forward."
Meanwhile, Mr Corbyn said there was a "greater understanding" from the public that the country "cannot go on with underfunded public services".
The polls will open at 07:00 GMT.
Other parties have been travelling the country on the last day before the election to win support from undecided voters.
Liberal Democrat leader Jo Swinson said votes for her party could stop Brexit, adding: "Our country can be better than what Boris Johnson and Jeremy Corbyn are trying to say is the only way forward."
The SNP's Nicola Sturgeon said a vote for her party was a vote to stop further cuts to public services and to "stop Scotland being dragged out of the EU against its will".
Nigel Farage warned against Mr Johnson's deal to leave the EU, calling for voters in Leave seats to back his Brexit Party.
And Green Party co-leaders Sian Berry and Jonathan Bartley urged voters to make it a moment of political reckoning on the climate, saying their party would make sure proper action was taken to meet carbon emission targets.
Talking to the BBC's political editor Laura Kuenssberg, Mr Johnson said he thought the election result would be "very close", and that "every vote counts".
Asked if he deserved to win, he said: "I do think that we have the best programme for the country, we have an amazing agenda. We want to unite and level up across the country."
Mr Johnson said the Conservatives' plans - including a law to ensure extra funding for the NHS every year and 20,000 new police offices - were "fantastically ambitious".
He added: "We can achieve all of these things. But we can't if our politics is paralysed by Brexit. We have to move it forward."
Asked about his reaction to the photo of a sick boy who had to sleep on the floor of a hospital due to a lack of beds, Mr Johnson said: "Obviously I think that anybody who experiences a bad time in the NHS has my full, full sympathies.
"We've all been there and anybody who has had a bad experience in A&E will know exactly how that family feels, and that is why I want to concentrate on getting cash into the NHS, taking the country forward."
But he reiterated that "only if you get Brexit done [can you] move the country forward".
Also speaking to Laura Kuenssberg, Mr Corbyn said he had a "hunch" that the polling experts - who have predicted a solid leader for the Conservatives over Labour - "may just have got it wrong".
"We have travelled all round the country and the enthusiasm of our party's supporters working together to get out there with our message is incredible - and I think that message is getting through," he said.
"I think the support is growing and there is a greater understanding that we cannot go on with underfunded public services and a government that has not been straightforward with us on Brexit or the trade talks with the USA."
Asked about candidates who have expressed concerns about negative feedback on the doorsteps - including a leaked recording of shadow health secretary Jon Ashworth casting doubts on Labour's chances in the poll - Mr Corbyn said: "You show me a candidate at any election that isn't worried from any party.
"Being a candidate means you get worried. But I tell you what, we are going to win this thing."
If there is a Labour government on Friday morning, Mr Corbyn said the first thing he would do was "deal with the worst levels of poverty in Britain" - namely the homeless - saying: "Something must be done very quickly, very urgently and that is what we are going to do."
Follow election night on the BBC
- Watch the election night special with Huw Edwards from 21:55 GMT on BBC One, the BBC News Channel, and BBC iPlayer
- It will also be shown on BBC World News and streamed live on the BBC News website internationally
- As polls close at 22:00, the BBC will publish an exit poll across all its platforms, including @bbcbreaking and @bbcpolitics
- The BBC News website and app will bring you live coverage and the latest analysis throughout the night
- We will feature results for every constituency as they come in with a postcode search, map and scoreboards
- Follow @bbcelection for every constituency result
- From 21:45 GMT, Jim Naughtie and Emma Barnett will host live election night coverage on BBC Radio 4, with BBC Radio 5 live joining for a simulcast from midnight