Principal vs. Interest: How It Works for Credit Cards and Loans

Most people have some debt. In fact, the average consumer carried $105,444 in 2025, according to Experian. That's a big number, and if you're making payments and wondering why you're not making progress repaying your debt, interest is likely the culprit.

The principal is the amount you originally borrow or charge, while interest is what the lender charges you to borrow money. The lender applies a portion of every payment you make to the principal, and the rest goes toward interest.

You can save money and pay off your debt faster by understanding how principal and interest work.

What's the difference between principal and interest?

When you take out a loan or make a purchase with a credit card, that initial amount is your principal. For example, if you take out a $5,000 personal loan, your loan principal is $5,000.

Interest is the fee you pay to the lender to borrow money. Typically, the cost of borrowing is expressed as an annual percentage rate (APR), or the yearly cost of the debt stated as a percentage. On loans, the APR includes both the interest rate and certain lender fees, so it reflects more than interest alone. On credit cards, the APR is the interest rate.

When you use a credit card or a loan, you don't only repay what you originally borrowed. You repay the initial amount plus interest.

The longer it takes to repay your debt, the more you'll end up paying in interest, increasing the cost of borrowing money.

Read more >> What's the Difference Between APR and APY?

In context: Experian's average consumer debt
$105,444 — average total debt per consume
$21,603 — the same average, excluding mortgage debt

Most of that gap is mortgage debt. So if you don't own a home, look at $21,603 instead: credit cards, auto loans, student loans, and personal loans all together. It actually fell 3.3% in 2025, which makes it one of the rare debt numbers going the right direction.

How do principal and interest work on installment loans?

Installment loans, like auto loans, student loans, and personal loans, give you an upfront lump sum of cash that you agree to repay in monthly installments for a set period.

During the early months of your repayment, a larger chunk of your payments goes toward interest. Over time, as you chip away at the balance, more of the payment amount goes toward the principal through a process known as amortization.

How it works: Loan interest

For example, say you take out a $10,000 personal loan with a repayment term of two years at an average 11.86% APR, as reported by the Federal Reserve. With that rate, your monthly payment would be $470.08.

With your first payment, $98.83 would go toward interest, and $371.25 would go toward the principal.

By the last month of your loan term, just $4.60 would go toward interest, and $465.48 would go to the principal.

Over the life of the loan, you'd repay a total of $11,281.95. Interest charges would add over $1,200 to your overall cost.

Run the numbers >> Use Kikoff's auto amortization calculator to see how much of each payment goes to interest versus principal over the life of your loan.

How do principal and interest work on credit cards?

Credit card debt works differently than installment loans. Instead of a fixed repayment schedule, credit cards are a form of revolving credit. You can borrow, repay, and borrow again up to your credit limit.

The credit card company charges interest on the balance you carry from month to month. If you don't pay off the balance in full by the payment due date, interest can accrue rapidly.

How it works: Credit card interest

Say you’ve charged $5,000 on a credit card at the current average 22.15% APR reported by the Federal Reserve. Assuming a 3% minimum, your first payment would be $150.

If you keep paying that flat $150 every month and add no charges, it would take four years and five months to clear the balance. And you'd repay a total of $7,834.05 — more than $2,800 on top of what you charged.

Pay the shrinking 3% minimum instead, and the payoff stretches out for decades.

Read more >> Why Paying Only the Minimum Hurts Your Credit

Ways to reduce interest charges

Reducing interest helps you keep more of your hard-earned money. There are a few ways to save on interest:

1. Pay more than the minimum. Anything above the minimum goes to principal, and a smaller principal means less interest accrues next month. Even a small amount compounds in your favor over time.
2. Pay credit cards off in full. Cards give you a grace period, so a balance paid off in full by the due date generally costs nothing in interest.
3. Consider consolidating. Moving high-interest debt to a 0% or low APR balance transfer card or consolidation loan can shrink both your rate and your payment. Just make sure to factor in transfer fees, and note the revert rate after the promotional period ends.

Bottom line

Every payment splits two ways: some goes to principal, the balance you actually borrowed, and some goes to interest, which is the cost of borrowing it. Interest buys you nothing. Anything you can shift toward principal shrinks the balance, and a smaller balance generates less interest next month.

That's the whole mechanism behind reducing what you pay on interest. It's also why paying on time matters twice over: You avoid late fees and added interest, and you build the credit history that gets you a lower rate next time. Kikoff's Credit Account reports your on-time payments to all three credit bureaus, with no hard credit check and plans starting at $5 a month.