"The commission held an engagement with the president... and subsequent to that the president then announced his intention to have elections before the end of May," Independent Electoral Commission chairman Glen Mashinini told reporters.
"We normally do it on a public holiday on a Wednesday. It will be one of those Wednesdays within the month of May after the 7th of May."
Ramaphosa, a former trade unionist and wealthy businessman, is expected to announce the election date in February.
At the last national elections, held in 2014, the African National Congress won 62 percent of the vote, the DA won 22 percent and EFF took six percent.
In local elections in 2016, ANC support fell to 53 percent -- pointing to a fiercely contested vote next year.
An October poll by Afrobarometer suggested 48 percent of South Africans would vote for the ANC, with the DA and EFF tied on 11 percent each.