Home Secretary Theresa May has agreed to waive the fee for gay couples who entered into a civil partnership before same sex marriage was available and now wish to convert their union.
The news comes a week after the Government announced the "straightforward" conversion process would be possible from December this year.
Speaking in the Commons today, Culture Secretary Sajid Javid said that charging those for whom marriage was not an option at the time would be "unfair".
He added: " The Government will be laying today the draft regulations for the conversion of civil partnerships to marriage. The cost of conversion, the Government had previously said it would be on a costs recovery basis...we had indicated about £100.
"I'm happy to say that in almost all cases it will be £45.
"I can further say I do think it would be unfair on couples that are in civil partnerships before marriage of same sex couples was available... to charge them this, so I'm pleased also to announce that the Home Secretary has agreed to waive the conversion fee for one year from December 10."
Last month, Mr Javid wrote in Pink News: "We've made the process of conversion as straightforward as possible.
"Couples will simply have to attend a Register Office and sign a declaration that they both wish to convert their civil partnership to a marriage in front of the superintendent registrar. That's it."
There was also good news for married transgender people, who will now be able to change their legal gender without ending their marriage if their husband or wife agrees.
But civil partnerships are not to be extended to straight couples after a report said three quarters of those who replied to a consultation were against the move.
It prompted accusations of a betrayal from human rights campaigner Peter Tatchell who said the Government was "maintaining legal discrimination" against straight partners.
"In a democracy, we should all be equal before the law," he added.