Failing to keep up with tax payments now could lead to an expensive surprise come next spring. As of Oct. 1, the Internal Revenue Service is charging 8% interest on estimated tax underpayments, up from 3% two years ago, the Wall Street Journal reports. The increase is one of the many effects of rising interest rates.

These higher penalties, which can run in the hundreds or even thousands of dollars, are particularly relevant for gig workers and consultants who don’t have taxes withheld and figure they can pay their taxes come April. People who get steady paychecks with tax withholding could also be affected if they have additional income and get the math wrong.

For most taxpayers, their employer withholds taxes in every paycheck, with the majority due for a tax refund for having overpaid. Still, the IRS assessed more than $1.8 billion in penalties for underpaying estimated taxes on nearly 12.2 million individual returns in fiscal year 2022.

Beyond underpayment penalties, the higher total tax bills for millions of Americans increase the risk that many won’t be able to pay their full balance in April. Failing to pay all of your tax bills can lead to more penalties and—in the worst case—IRS collection actions, including liens and levies.