The pub chain has raised the equivalent of £850,000 every year for CLIC Sargent since it became a charity partner in 2002.
Over the last 14 years staff and customers have carried out countless fundraising events for CLIC Sargent.
Major recent events include a national pub-wide darts competition in March, which raised more than £200,000 and the annual Kick five-a-side tournament, in which 550 teams from pubs around the UK took part, raising more than £460,000.
Hundreds of staff are expected to add to the fundraising total on 25 May, when they will be donning fancy hairpieces as part of CLIC Sargent's Wig Wednesday event.
Where it all began
The partnership between J D Wetherspoon and CLIC Sargent began when pub chain founder Tim Martin coincidentally sat opposite the then chief executive of the charity on a train.
They struck up a conversation and Tim was inspired to launch a partnership, with an initial target of £500,000. The reaction from staff was overwhelmingly positive, causing the fundraising target to be raised each year.
J D Wetherspoon chairman Tim Martin said: “We are extremely proud of our association with CLIC Sargent. Since 2002 our staff and customers have brilliantly supported our fundraising efforts.
“The fact that we have now raised £12million for such a wonderful charity is thanks to them. We look forward to raising even more money in the future.”
CLIC Sargent Chief Executive Kate Lee said: “We are truly blown away by this spectacular fundraising total. The money raised by J D Wetherspoon helps us provide vital support for young cancer patients. Hundreds of families will have benefited directly from these funds."