Michael Adebolajo, 29, and Michael Adebowale, 22, will learn how long they face behind bars when they return to the dock at the Old Bailey, London, on February 20.
They are due to be sentenced by Mr Justice Sweeney, who said when they were found guilty of the horrific killing that he would wait for a key decision by appeal court judges over whole life tariffs.
The appeal judges' ruling has not yet been announced.
Fusilier Rigby, 25, was run over and then butchered by the pair in front of onlookers in Woolwich, London, on May 22 last year.
The men, who declared they were soldiers of Allah, targeted him because he was wearing a Help For Heroes hooded top and they assumed he was a serviceman.
A panel of five judges, headed by the Lord Chief Justice Lord Thomas, heard argument at the Court Of Appeal on January 24 on behalf of Attorney General Dominic Grieve, that tariffs which mean criminals have to spend the rest of their days behind bars are not "manifestly excessive or wrong in principle".
The Attorney General referred the case of triple killer Ian McLoughlin to the court on the grounds that it was "unduly lenient" and should be increased.
Mr Justice Sweeney had given McLoughlin a life sentence with a minimum term of 40 years.
The appeal judges were also asked to rule on a sentence challenge by double killer Lee Newell, who is facing dying behind bars for murdering child killer Subhan Anwar in prison.
Those serving whole-life terms in England and Wales include Moors Murderer Ian Brady, serial killer Rosemary West, and Mark Bridger, who murdered five-year-old April Jones.
The sentences were deemed a breach of human rights following a successful appeal to the European Court of Human Rights by murderers Jeremy Bamber, Douglas Vinter and Peter Moore.