"I was looking on Craigslist and I just happened to come across an ad that struck my eye," Calderbank told CBS New York. "Somebody was asking for a kidney for their wife."
The post was authored by Kay Saria, whose wife, Nina, was in need of a kidney.
Calderbank said he lost his wife, Jessica, to kidney failure four years ago after her body rejected a donated organ from a cadaver.
"I was meant to see that," Calderbank said. "I believe that Jessica somehow -- or karma -- whatever it is. Put that in the wrong spot because that's the only place I go on the computer anyways."
Nina Saria said she hadn't expected a reply on the post.
"My husband came up with the idea to put an ad on Craigslist," she told NJ.com. "I got a lot of prayers, but no one to donate. I wanted to give up, but Kay didn't."
Saria soon received a message from Calderbank.
"I said 'look -- I know I'm a match.' She said 'how do you know that?'" Calderbank said. "I said there's no way that I saw your ad by accident."
The surgery is scheduled for Dec. 1 at University of Pennsylvania Hospital.
"I'm scared to death," he said. "I've never had any medical problems and I am, on purpose, going to have my body opened up and have a part taken out. But I'm doing it because I want to help."
Saria said she is hoping Calderbank's sacrifice inspires others to donate.
"Not a lot of people know much about kidney donation," Saria said. "I really wanted people to know that he was a stranger from Craigslist and now we're friends. People can't believe how someone can be so nice and brave. So, I think we need to spread the word around that donating a kidney is not deadly and maybe we can save more people who are on dialysis like me."
