U.S. Rep. John Conyers announces his retirement.

WASHINGTON — The process of filling the seat left open by the retirement of Michigan Democratic Rep. John Conyers could take some time to sort out and cost a good bit of money.

By law, the governor is required to call a special election to select someone to fill out the remainder of the congressman’s term, which ends Jan. 3, 2019.

Michigan Gov. Rick Snyder can schedule that election whenever he wishes, though it often comes on the date of the next regularly scheduled election — which, at present, is May 7, 2018, when there will be balloting for local boards and millage rates.

Dec. 5: Rep. John Conyers announces he will ‘retire today’ from congressional seat

Dec. 5: Alaska’s Don Young to become most senior member of Congress after Conyers’ retirement

But because it’s a House seat, that also means having a primary election first to decide who would run in a general election. That’s what happened in 2012, for instance, after former congressman Thad McCotter, a Republican from Livonia, Mich., stepped down in July.

Kerry Bentivolio won a September primary to be the Republican nominee to both fill out McCotter’s unexpired term and to take the seat in the next Congress. In the November general election, however, Democrat David Curson won the race to serve out the remaining six weeks of McCotter’s term while Bentivolio won to replace McCotter in the next Congress.