Betfair are offering London Marathon runners the chance to place a bet on themselves.
The Back Yourself campaign will give runners a £20 free bet with winnings going to charity.
The site will be open to participants aged 18 or older from Wednesday April 20 until midnight on Saturday April 23.
The 2016 London Marathon takes place on Sunday April 24.
Runners will be asked to enter a number of details about their running history, training efforts, and target time so that the odds can be calculated. Runners can then place their £20 free bet.
If the target time is reached, the runner will need to send a screenshot of their official time to Betfair, and the bookmakers will donate the winnings plus their £20 stake to the runners’ fundraising page.
If the target time is missed, the £20 free stake will be donated to Cancer Research UK.
As well as marathon runners, Betfair are encouraging customers who are embarking on unique and inspiring challenges, to back themselves to achieve them.
This could be anything from roller-skating around the world to canoeing from the South Pole to the North Pole.
Betfair spokesman Naomi Totten said: “We’re thrilled to relaunch our Back Yourself campaign as it provides a way for people who are reaching for the stars to add an extra incentive to their challenge by guaranteeing them a large donation should they manage to complete their epic adventure.”
Betfair customer Rupert Arup has placed a bet on himself ahead of this year’s London Marathon.
He said: “This is my first marathon and, honestly, the training has been the hardest thing I’ve ever done in my life.
“My sister and I are incredibly proud to be running on behalf of the National MS Therapy Centre who have been such a fantastic support for our family since my father was diagnosed with Multiple Sclerosis.
“With just five days left until the big day there’s not really much else I can do in terms of training so my main focus is the final push on fundraising to ensure we raise as much money as possible.
“So Betfair’s Back Yourself campaign comes at the perfect time and also adds an extra incentive for me to hit my target on the day.”