Registration was first extended by two months after it got off to a slow start in October because of a dearth of registration machines and problems operating them.
An estimated 53 million Nigerians have registered to vote in April elections and that figure will rise after full results of the registration process are collated, the head of the INEC said on Tuesday.
Nigerians have lined up for hours at registration posts in the past few days to register and ensure they can vote in April polls that should mark Nigeria's first democratic transition from one civilian government to another.
"We have 53 million registered voters so far and we have not finished counting," Maurice Iwu said.
About 35 million people voted in the last presidential election in 2003 and the INEC had said it expected to register 70 million voters for this year's poll.
In the past few days the Nigerian authorities have offered a series of incentives, such as days off work for public servants, to encourage potential voters to sign up.
Some state authorities have threatened to deprive citizens who do not sign up of access to basic social services such as healthcare and schooling.
The initial six-week extension would have meant that registration closed on January 30.
Nigeria's 2006 census figure put the nation's population at just over 140 million. Figures showing what percentage of that total are adults eligible to vote have not yet been made public.
The first two months of registration were beset by a myriad of technical and logistical problems ranging from a lack of public awareness to registration machines that were neither fully functional nor sufficient in number.
The April vote is being billed as the first transition in Nigeria's history, long punctuated by military coups, from one democratically elected civilian administration to another.