Sergeant Alexander Blackman, 42, from Taunton in Somerset, was sentenced to seven years on Tuesday for diminished responsibility manslaughter following the recent quashing of his murder conviction.
As a result of time already served since his original conviction in November 2013, the decision of five judges at the Court Martial Appeal Court means it is likely Blackman could be freed next month.
He has already spent almost three-and-a-half years in prison.
Announcing the seven-year term, the panel of judges, headed by Lord Chief Justice Lord Thomas, said: "As with any person sentenced to a determinate term, his release will ordinarily be at the halfway point of the sentence."
At a hearing last week the judges heard that Blackman's legal team had calculated he would have served the equivalent of a seven-year determinate sentence by April 24.
Blackman watched the proceedings via video-link from prison.