If you paid all your property taxes early or expected the tab to be the same amount paid in July or October, or thought you had credits, you are in for a surprise.

Computers do make mistakes. As the saying goes, garbage in garbage out. So, if you, like Mayor de Blasio, had property tax credits on your last two bills, it was probably a mistake.

“There was a technical glitch that caused credits to incorrectly appear on some people’s second- and third-quarter property bills,” an NYC Finance Department spokesman explained in an e-mail. “The amounts due are correct and no one owes any more or less as a result. The issue has since been resolved and the Department of Finance will replace erroneous bills for affected properties and send notifications to property owners.”

De Blasio is also among those who will likely have to dig deeper into his pocket now that there are new tax rates set by the City Council. This is causing a mid-year correction and some will pay more, and some less.

While this happens from time to time, it still causes confusion, especially if you don’t look at your bill. And when there are head-scratching credits, like those that appeared on de Blasio’s last two bills for one of his Park Slope properties, it is hard to know what you owe.

According to a Council spokesperson, the average tax rate citywide remained the same.

But one- to three-family homeowners, utilities and commercial buildings will have to pay a bit more than they expected.

Class 1 home bills will go up 1.2 percent, compared to what would have been a larger 6.3 percent increase if the Council had not rejiggered the tax rates.

For instance, Jeffrey Epstein’s luxury townhouse at 9 E. 71st St. was all paid up for the tax year after shelling out the entire $347,021.16 — which was everything due in July for the full ’19-20 tax year. The new bill now due Jan. 2 is for an additional $4,114 — nearly the entire tax bill for Park Slope brownstones owned by de Blasio.

De Blasio is also getting hit with bills for an additional $49.72 on each of his two Park Slope homes — now being rented out — for total annual taxes of $4,246.52 each.

The home on 11th Street where he and the family resided before moving to Gracie Mansion is worth $1.78 million. It is being rented out for roughly $5,000 to $6,000 per month.

But while looking at the bill, I noticed his last two quarterly bills showed credits on each bill for the entire half-year’s taxes — $1,049.20 — caused by what Finance now says was a computer error.

The other nearby home, which has two apartments rented out for about $5,000 per month each, has a market value of $1.944 million.

Both homes have an assessed value of $20,062 and now the same low taxes. That’s because City politicians tend to favor the thousands of voters who live in one- to three-family homes — except for those like the late Epstein who are in wealthier ’hoods like the Upper East Side where values are sky-high.

Those who pay taxes in Westchester and Nassau are swooning right now as their tax tabs for homes worth $1.5 million to $2 million are closer to $30,000 to $40,000 per year — albeit they send their kids to the free public schools.

Still, the winners of the Council’s latest tax rate changes are multifamily apartment buildings, including co-op and condo owners, and suffering apartment building owners, who will get a slight break. These Class 2 properties have a 1.1 percent decrease compared to what would have been a 0.8 percent increase without the “re-adoption” of tax rates, the City Council spokesperson e-mailed.

Additionally, the Class 4 commercial group has a small, 0.2 percent increase versus what would have been a 2.1 percent decrease had the Council not reset the rates.

But remember, the Class 3 utilities that pay more often pass those increases onto rate-paying customers.

So as long as the City keeps spending your dollars like the world is ending and has computer bugs, the Grinch will get you every which way.