It was the 73rd birthday of Dr William Wan yesterday and he celebrated by doing 100 push-ups - all in the name of charity.

His feat raised $237,000 for the Prison Fellowship Singapore, which he co-founded 46 years ago in support of inmates and ex-offenders on their journey towards successful reintegration into society.

Dr Wan, who is general secretary of the Singapore Kindness Movement, said he had been training for the challenge since early last month. The challenge was streamed as a 30-minute Facebook live event.

"The money raised so far within less than a week is very significant. And I know that many more will be giving... I have confidence that by the end of the month, we will reach our target (of at least $730,000)," he said.