Election officials took the decision on the advice of security officers concerned about the Islamist-led insurgency in the north-east, he said.
The six-week delay was not a “big deal”, he said on national television.
The opposition claims Mr Jonathan pushed for the polls to be delayed because he feared defeat.
The elections have been rescheduled for 28 March.
Analysts say the election is the most closely contested since military rule ended in 1999.
Mr Jonathan and his People’s Democratic Party (PDP) are facing a strong challenge from ex-military ruler Muhammadu Buhari and the All Progressives Congress (APC).
Elections for state governors and assemblies slated for 28 February have been moved to 11 April.
Mr Jonathan said he would “happily” give up the presidency if he lost.
The “international community” sometimes saw the postponement of elections in African states as an attempt by the incumbent to cling to power, he said.
“This is not the case in Nigeria,” Mr Jonathan added, giving an assurance that the government elected on 28 March would be sworn in by 29 May in accordance with the constitution.
The US, UK and Canada have expressed concern about the postponement of the polls in Africa’s most populous state and main oil producer.
On Tuesday, Nigeria’s former President Olusegun Obasanjo added his voice to the concerns, telling London’s Financial Times newspaperthat he hoped Mr Jonathan was “not going for broke and saying: ‘Either I have it or nobody has it’.
“I hope that we will not have a coup… I hope we can avoid it,” Mr Obasanjo said.
Mr Jonathan said the Independent National Election Commission acted within the constitution when it postponed the polls.
Difficulties in distributing voter cards and security concerns were legitimate reasons for the delay, he said.
“I was not consulted and I don’t want to be consulted,” Mr Jonathan added.
Mr Jonathan is contesting his second presidential election. His presidency has been marred by powerful PDP members defecting to the newly formed APC, fuelling speculation that he could be defeated in the election.
He has also been strongly criticised for failing to curb the insurgency in the north-east by militant Islamist group Boko Haram.
Thousands of people have died as a result of the conflict over the past six years, while more than three million people have been forced from their homes.
The militants control a large stretch of land in north-eastern Nigeria and have stepped up attacks on neighbouring countries.