A debt collector can charge interest on what you owe only if the original credit agreement expressly allows it or a specific law authorizes it. That is the rule under the Fair Debt Collection Practices Act, and it decides almost every dispute about interest on a collection account. If a collector is adding interest that neither your contract nor a statute backs up, the charge is illegal.1Office of the Law Revision Counsel. 15 USC 1692f – Unfair Practices
The Two Legal Bases for Interest
The FDCPA says a collector cannot collect any amount, “including any interest, fee, charge, or expense incidental to the principal obligation,” unless the amount is “expressly authorized by the agreement creating the debt or permitted by law.”1Office of the Law Revision Counsel. 15 USC 1692f – Unfair Practices Two paths, and a collector needs one of them.
The first is your original contract. Credit card agreements, auto loans, and personal loans usually spell out an interest rate, how it compounds, and whether the rate can rise after default. If the contract allowed interest to accrue on overdue balances, a later collector who acquires or is assigned the debt can keep applying interest on the same terms. If you still have the agreement, pull it out; the answer to whether interest is authorized, and at what rate, is in there.
The second path is a statute that independently authorizes interest on the obligation. Post-judgment interest is the most common example. The CFPB reads “permitted by law” strictly: a charge is not permitted simply because no law forbids it. Silence in the statute books is not authorization.
Interest After a Charge-Off or Debt Sale
A charge-off is an accounting move by the original creditor. The debt itself survives, and so do the contract terms attached to it. If the agreement allowed interest to keep accruing, the charge-off by itself does not stop the clock.
When the original creditor sells the account to a debt buyer, the buyer generally takes whatever rights the contract gave the creditor, including the right to charge the contractual interest rate. Courts have generally accepted this. In one federal case, a court held that a debt buyer did not violate collection law by accruing interest after charge-off because the original contract expressly permitted it.
The harder case is when the original creditor had stopped billing interest before selling the debt. Some courts have treated that as a possible waiver of the right to collect future interest; others have gone the other way. If a debt buyer suddenly starts adding interest that the original creditor had frozen, that is worth pushing back on. Check the contract for whether the creditor could resume interest, and look at the last statements you received from the original creditor to see whether interest was still being applied.
Interest After a Court Judgment
Once a creditor sues and wins, post-judgment interest starts running on the judgment amount from the date it is entered, and it keeps running until the balance is paid. This is separate from any interest the original contract carried, and once judgment is entered, the judgment rate typically replaces the contract rate.
In federal court, the rate equals the weekly average one-year constant maturity Treasury yield for the calendar week before the judgment, compounded annually.2Office of the Law Revision Counsel. 28 USC 1961 – Interest State courts use their own formulas. Some set a flat statutory rate; others tie the rate to a financial benchmark and adjust it periodically. State post-judgment rates generally fall somewhere between 4% and 17%, and a few states allow higher rates for certain kinds of judgments.
If a collector is trying to collect on a judgment, ask for the specific judgment interest rate and check it against your state’s published schedule. The rate may be higher or lower than what your original contract carried, and the difference can be significant over time.
Get the Itemized Breakdown
You do not have to guess how much of what a collector is demanding is interest. Within five days of first contacting you, a debt collector must send a written validation notice showing the amount of the debt and the name of the creditor.3Office of the Law Revision Counsel. 15 USC 1692g – Validation of Debts Under the CFPB’s Regulation F, the notice has to go further: an itemization showing the balance as of a specific date, plus a line-by-line breakdown of interest, fees, payments, and credits applied since that date.4Consumer Financial Protection Bureau. Regulation F 1006.34 – Notice for Validation of Debts Even if no interest has been added, the collector must include the interest line and show it as zero.
This itemization tells you exactly how much is principal, how much is interest, and how much is fees. If the collector cannot produce it, or the interest figure does not match what your contract would allow, you have concrete grounds to challenge the amount.
How to Dispute Interest That Looks Wrong
Act within the 30-day window after you receive the validation notice. Send a written dispute, ideally by certified mail with return receipt, saying that you dispute the amount and explaining why. Once the collector receives a written dispute, it must stop collection activity until it sends you verification of the debt.3Office of the Law Revision Counsel. 15 USC 1692g – Validation of Debts Calls and letters can continue during the 30 days only until your written dispute arrives.
While you wait, dig up the original credit agreement. Check the interest rate, whether it was fixed or variable, and whether the contract allowed the rate to change after default. Compare those terms against what the collector is claiming. If the collector is applying a higher rate than the contract allows and no court judgment set a different rate, the excess is unauthorized under the FDCPA.1Office of the Law Revision Counsel. 15 USC 1692f – Unfair Practices
If direct pushback does not resolve it, file a complaint with the CFPB, which oversees debt collection practices. For larger sums or complicated fact patterns, a consumer law attorney can tell you whether you have grounds to sue. Most FDCPA lawyers work on contingency or rely on the statute’s fee-shifting provision, so the upfront cost tends to be minimal.
What You Can Recover If the Collector Was Wrong
A collector who charges unauthorized interest is violating the FDCPA, and you have a private right of action. If you win, three categories of damages are available. First, actual damages, which can include financial losses, emotional distress, and lost wages tied to the collector’s conduct. Second, statutory damages of up to $1,000 per lawsuit, which a court can award even without proof of specific harm.5GovInfo. 15 USC 1692k – Civil Liability Third, attorney’s fees and court costs if you prevail.
The $1,000 statutory cap is per lawsuit, not per violation. Multiple violations in a single collection effort still yield a maximum of $1,000 in statutory damages, though actual damages have no cap. In a class action, statutory recovery for the class beyond the named plaintiffs is capped at the lesser of $500,000 or 1% of the collector’s net worth.5GovInfo. 15 USC 1692k – Civil Liability
Who Counts as a Debt Collector
The FDCPA’s rules on interest do not apply to every party that might contact you about a debt. The statute defines a “debt collector” as someone whose principal business is collecting debts, or who regularly collects debts owed to another.6Office of the Law Revision Counsel. 15 USC 1692a – Definitions Third-party collection agencies clearly qualify.
Original creditors collecting their own debts are generally outside the FDCPA. If your bank or card issuer is calling directly, the federal interest restrictions do not apply to them, although state laws may.
Debt buyers sit in a gray zone. In Henson v. Santander Consumer USA, the Supreme Court held that a company purchasing and collecting debts for its own account does not fall under the “debts owed another” prong of the definition.7Supreme Court of the United States. Henson v. Santander Consumer USA Inc. Many dedicated debt buyers still qualify under the separate “principal purpose” prong, because their entire business is buying and collecting defaulted debts. Most large debt buyers remain bound by the FDCPA, but whether a specific company is covered depends on how it does business.