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Overpay the Mortgage or Keep Cash in a High-Yield Account? Compare After-Tax Rates

By Smart Budget Sheets November 10, 2026
Overpay the mortgage or keep cash in a HYSA: compare after-tax rates.

The usual rule is to compare your mortgage rate with what the savings account pays. The better comparison uses after-tax numbers.

Savings interest is taxed

US savings interest is taxed as ordinary income. $10,000 at 4.5% earns $450 a year. In a 22% federal bracket, that is about $351 after federal tax (more if your state taxes it too). The after-tax rate is about 3.5%.

Mortgage overpayments save the full rate

Overpaying $10,000 on a 6.5% mortgage saves about $650 of interest in the first year, and that saving is not taxed. The only exception: if you itemize and deduct mortgage interest, the real saving is somewhat lower. Most households take the standard deduction.

So, by rate

  • Mortgage at 3%: $300 saved vs about $351 after tax in savings. Keeping the cash wins slightly, and you keep the flexibility.
  • Mortgage at 6.5%: $650 vs about $351. Overpaying clearly wins on rate.

Rate isn’t the only question

  • Money paid into a mortgage is hard to get back out. Keep your emergency fund first.
  • High-interest card debt beats both.
  • An employer retirement match usually beats both too.
  • Savings rates change; a fixed mortgage rate does not.

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General information, not financial advice. Figures are rounded examples.

#personalfinance #budgeting #mortgage
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