Free stuff: That’s essentially the topline argument for socialist policies.

In all fairness, it’s a pretty good one.

Who doesn’t like freebies?

Free food.

Free drinks.

Free gifts while supplies last.

Even grandma pockets the free Sweet’N Lows at the diner.

Zohran Mandani is well aware of this inherent human trait, and he’s focused a fair amount of his campaign on promising gifts to the masses.

The bread-and-circuses approach has placed him solidly in the lead, with promises of free day care, free buses, free legal advice for illegal migrants and more.

This week, he launched an online “savings calculator” that claims to tally how much you’ll personally gain in Mayor Mamdani’s utopia (in exchange, of course, for adding your name and email to his campaign mailing list).

But as the old Thatcherism goes, the problem with socialism is that you eventually run out of other people’s money.

And in New York City, the public kitty is already drying up.

According to State Comptroller Tom DiNapoli’s recently released annual report on the city’s finances, the projected budget gap for the first three fiscal years Mamdani could serve as mayor is a whopping $17.1 billion.

That’s a huge gulf between how much city revenue we can expect to collect versus how much we spend — before piling on the costs of his pricey promises.

To be clear, this isn’t on Zohran.

It’s the very real financial outlook he may well inherit.

The idea that New York can simply eat the costs of his shiny new programs while under this stress it not simply bad policy, it’s financially impossible.

That means Mamdani’s early mayoralty may very well be forced to focus on program cuts, rather than rainbows and sprinkles.

Mayor Eric Adams began to address this reality with some modest belt-tightening during this year’s budget dance, shaving a point or two off the shortfalls.

This, of course, angered many of Mamdani’s progressive City Council allies.

Come next year, Mamdani could have his hands on the steering wheel while the Council’s Progressive Caucus has its foot on the gas pedal — and taxpayers might be in for a demolition derby of a ride.

Luckily, Zohran has a plan for that: We might not need our cars at all anymore. We’ll all just ride the bus!

“Free Buses” is a concept so outrageously expensive that even MTA Chief Janno Leiber — a hall-of-fame punter of public dollars in his own right — dismissed it as some kooky experiment.

The city’s Independent Budget Office pegged the cost at $652 million — more than the city spends on its entire Department of Parks and Recreation, an agency so strapped for cash it faced its own $62 million in cuts this year.

So if Mamdani follows through on his free-bus scheme, he’ll have to do what City Hall now does to cover its $95 million “Fair Fares” program for low-income New Yorkers: Cut an annual check to the MTA for nearly $700 million, to offset the loss.

And that’s just one of his plans.

Another big spend is his idea of universal childcare for babies as young as 6 weeks, staffed by caregivers paid “at parity” with public-school teachers.

The price tag, per Mamdani’s own campaign: $6 billion per year.

Where will that come from, in a budget that’s already billions in the red?

Sure, Mamdani’s Albany allies might kick in some cash — but nowhere near enough.

DiNapoli’s report found that the state, too, could be facing a budget gap of up to $2.2 billion, including a $100 million shortfall to 3K and Pre-K programs.

Then, expect big budget changes from Washington, DC: The GOP’s One Big Beautiful Bill Act will likely cut federal funding for NYC Health and Hospitals and the Department of Social Services.

Adams has set aside $8.5 billion in reserves and a $2 billion rainy-day fund — but that won’t last long in the face of Mamdani’s wishlist.

And it seems unlikely that a Mayor Mamdani would have the political juice to get those federal cuts restored.

Just last week, the city’s lone House Republican, Nicole Malliotakis, got right on the horn with President Trump and succeeded in reversing a proposed $187 million cut to anti-terrorism funding.

Is there any chance we’d see the Democratic Socialist go hat-in-hand to this White House seeking more money for the NYPD?

Not to mention the difficulty of getting back in Washington’s good graces on crucial funding issues like payments to our city hospitals, when — instead of complying with federal immigration law — Mamdani is pledging a new $100 million legal-aid program to help individuals fight it.

All this means that if elected, Mandani will face significant fiscal headwinds as he tries to make good on his promises.

Will prudence and restraint trump the easy impulse to tax and spend?

New Yorkers may have open minds, but not open wallets.

Joe Borelli is a managing director at Chartwell Strategy Group and former minority leader of the New York City Council.