High-Yield Savings vs. Paying Off Debt: Where Should Extra Cash Go?

For the past few years, anyone with a High-Yield Savings Account (HYSA) has enjoyed seeing regular monthly interest deposits. Earning 4.5% to 5.0% APY on liquid cash without risking a penny in the stock market feels great.

At the same time, millions of households carry mortgages at 6.5%, car notes at 7.5%, or credit cards at 22%. That raises a common question: If you have an extra $500 or $1,000 every month, should you put it into your savings account, or use it to pay down debt?

The Golden Rule: The Interest Rate Comparison

At its core, paying off debt delivers a certain, cost-equivalent return equal to the interest rate on the debt. If you pay down a 22% credit card, you are effectively saving a 22% charge by avoiding those charges.

• Debt above 8% (Credit cards, personal loans): Prioritise paying these off first. Few savings accounts or conservative investments can match a 15% to 25% interest cost saving.
• Debt below 4% (Older fixed mortgages or low student loans): Keeping cash in a 4.5% HYSA makes sense, as the cash earns more than the debt costs while keeping your funds liquid.
• Debt between 5% and 7% (Modern mortgages and auto loans): This is the grey zone where taxes make all the difference.

Don't Forget the Tax Hit on Savings Interest

Many savers forget that interest earned from bank accounts is considered regular taxable income by the IRS, HMRC, and state tax authorities. If your savings account pays 4.75% APY and you are in the 24% federal tax bracket (plus 5% state tax), your real return is:

Suddenly, that 4.75% yield is only putting 3.37% in your pocket. If you have an auto loan charging you 6.8%, you are losing money every single month by holding excess cash in savings instead of paying off the car.

The Practical 3-Step Strategy

1. Step 1: Build a 3-month emergency cushion first: Liquid peace of mind is priceless. Keep 3 months of baseline living expenses in your HYSA so an unexpected dental bill or car repair doesn't force you into new debt.
2. Step 2: Destroy all high-interest debt (anything over 8%): Throw every spare dollar above your emergency cushion at credit cards and personal loans.
3. Step 3: Split the difference on mid-rate debt: If your mortgage is at 6.5%, put 50% of your monthly surplus toward the loan principal, and 50% toward liquid savings or long-term index funds. You capture the psychological win of building wealth while chipping away at your debt.

Authoritative Banking & Tax Guidelines

• Federal Deposit Insurance Corporation (FDIC) — Deposit Insurance Overview ($250k Coverage)
• Internal Revenue Service (IRS) — Topic No. 403: Interest Received & Taxable Income