The MTA’s debt is a ticking time bomb that could force the authority to raise fares and cut service, a state watchdog said.

The agency’s annual debt bill will account for 22.5 percent of its operating expenses in 2023 — costing $4.2 billion that year alone, according to a new analysis by state Comptroller Tom DiNapoli.

By that time, the MTA’s total debt load will exceed $52 billion, up from $35 billion in 2019 and just $11 billion in 2000.

Without additional funding, paying those debts will fall on riders, who are already due for 4 percent fare increases in 2021 and 2023, according to DiNapoli’s analysis.

“Unless the MTA can change the way it does business and reduce costs . . . riders could be saddled with even higher fares and tolls than already planned,” DiNapoli said in a statement.

And things could get even worse if coronavirus dips into the MTA’s fare revenue, advocates warned.

“The gist of it is that the risk of debt is just the same for the MTA as it is to a person,” said John Kaehny, executive director of Reinvent Albany.

“You can’t afford to have anything go wrong. You can’t lose your job. The MTA can’t have any setback of any kind or you won’t be able to pay off your debt.”