Less than 20% of New York City voters cast ballots in Tuesday’s election, despite the introduction of early voting meant to boost turnout.

Unofficial City Board of Election results showed 723,462 denizens voted in the citywide public advocate’s race, a fraction of the roughly 4.7 million active registered voters living in the five boroughs — coming in at an estimated 15.15 percent.

It’s still higher than February’s special election for the same post, when 422,946 New Yorkers cast a ballot.

Tuesday was viewed as a low turnout year, as city denizens faced just one citywide election.

Voters chose to re-elect Democratic incumbent Jumaane Williams to another two years, and also decided on five ballot measures that will amend the City’s charter by a two-to-one ratio.

Statewide totals fared similarly dismal, as an approximated 26.32 percent hit the ballot box — 3,102,177 active voters of the 11,783,91 total registered active voters.

SUNY Albany political science professor Bruce Gyory acknowledged the low turnout as normal, dubbing it an “off, off year” as voters had neither a presidential, gubernatorial nor mayoral race to think about.

“What’s interesting is the difference between the turnout in the public advocate’s race and the amendment for rank choice voting, which was was 644,477 votes,” he told The Post, noting even less ballots were cast for the city charter amendments.

“My concerns is: here we had the most significant change in how New York City votes and it was geared toward a year that we have the lowest possible turnout. We ought to ask ourselves, is it smart to put such a major fundamental change in how New York City is going to conduct its elections when you’re guaranteed such a low turnout?”

Residents were also gifted nearly a week and a half of extra time to vote, thanks to early voting.

Although only 60,110, or 1.3 percent, of the city’s total registered voters took advantage of the perk.

The polls were opened ahead of Tuesday, starting Oct. 25 through Nov. 3.

Two percent of voters statewide, or 256,000 people, came out to the polls during that time period.

“It was a good year to work out the kinks because we didn’t know mechanically how it was going to work. Next year it would’ve been hard, as volume is the enemy of efficiency — with the presumptive notion that statewide you’re going to probably have a bigger turn out,” said Gyory.

Advocates similarly deemed the first year a success.

“Wait times were minimal – or nonexistent – and whatever minor hiccups happened, there was ample time for the Board of Elections to respond. This is how voting should be,” said Susan Lerner, Executive Director of Common Cause New York.