HYSA Compound Interest & Tax Drag Calculator – 1099-INT Federal & State Net APY

Calculate exact tax drag on High-Yield Savings Account interest (Form 1099-INT). Model federal and state marginal tax erosion, after-tax net APY, and compare against tax-exempt T-Bills.

Initial Cash Deposit ($)

Monthly Additional Savings ($)

Advertised HYSA Annual APY (%)

Savings Time Horizon (Years)

Federal Marginal Tax Bracket

State Marginal Income Tax Rate (%)

Annual Inflation Rate (%)

Net Effective After-Tax APY

3.33% Net APY

Down from 4.75% nominal APY

Cumulative Tax Drag (1099-INT)

-$3,180

Total federal + state tax paid

After-Tax Wealth Breakdown:

Projected After-Tax Ending Balance:$93,420

Net After-Tax Interest Earned:+$7,420

Real Purchasing Yield (After Inflation):+0.83%

State Tax Saved by Switching to US T-Bills:$636 State Tax Saved

The Form 1099-INT Tax Reality: Bank savings interest is taxed as ordinary income—NOT favorable capital gains rates. In high-tax states like California, New York, or New Jersey, a combined 35% to 45% tax bracket reduces a 5.0% HYSA down to just 2.75% take-home yield.

Compound interest and tax drag model based on statutory 2026 IRS ordinary income tax rates. State tax brackets vary by jurisdiction. Consult a CPA for personal tax planning.

Why Advertised HYSA Rates Suffer Significant Tax Drag

High-Yield Savings Accounts (HYSAs) from online banks like Marcus, Ally, Capital One, and Wealthfront offer attractive Annual Percentage Yields (APYs). However, many savers fail to anticipate the tax consequences: bank interest is fully taxable as ordinary income at your highest marginal federal and state tax rates.

How Form 1099-INT Tax Drag Erodes Cash Wealth

No Capital Gains Discount: Unlike stock investments held over 12 months which receive favorable 15% or 20% long-term capital gains rates, bank interest is reported on IRS Form 1099-INT and taxed at your top bracket (up to 37% federal plus state taxes).
Combined Marginal Tax Bite: A saver in California (9.3% state bracket) with a 24% federal bracket faces a combined 33.3% tax rate. An advertised 4.75% APY yields only 3.17% in actual pocketed cash.
Inflation Erosion: If annual consumer price inflation is 2.8%, an after-tax return of 3.17% delivers a razor-thin real net yield of just 0.37%.

The US Treasury Bill Alternative

For individuals residing in states with high income taxes, investing short-term cash reserves in 4-week, 8-week, or 13-week US Treasury Bills (T-Bills) is significantly more tax-efficient: under federal law (31 U.S.C. § 3124), US Treasury obligations are 100% exempt from state and local income taxes.

Frequently asked questions

When do banks issue Form 1099-INT?

Financial institutions are required by the IRS to issue Form 1099-INT to any account holder who earns $10 or more in interest during the calendar year.

Is interest in an HYSA subject to NIIT?

Yes. For individuals with Modified Adjusted Gross Income exceeding $200,000 ($250,000 for married filing jointly), bank savings interest is subject to the additional 3.8% Net Investment Income Tax (NIIT).

How do T-Bills compare to HYSAs after taxes?

Because US Treasury Bills are completely exempt from state and local income taxes, a 4.8% T-Bill yield in New York or California can deliver a higher after-tax take-home return than a 5.2% commercial bank HYSA.

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