Participating charities are hoping to bring in £1.5m in new donations this week to add to £3m already raised. The new donations will be matched pound for pound by the Reed Foundation to give a total pot worth £6m.
The Big Give ran its first matched funding challenge last year, raising £2m in 45 minutes, with an average donation of £1,400.
The scheme was criticised last month for being too complicated and for misleading charities about its ‘double your donation' pledge.
Alec Reed, founder of the Reed Foundation, last week told Third Sector he had set up the complicated system so that charities whose fundraisers who were intelligent and "on their toes" would benefit from the foundation's money.