# Boomers Hold $90T in G-Shaped Economy, Social Security Taxable at 70

> At 70, boomers' cash earns interest that silently taxes Social Security benefits via 1984 IRS formula.
- Title: Boomers Hold $90T in G-Shaped Economy, Social Security…
- Summary: At 70, boomers' cash earns interest that silently taxes Social Security benefits via 1984 IRS formula. Higher Treasury yields push retirees into taxable…
- Keywords: boomers, social security, treasury yields, irs formula, combined income, g-shaped economy, retirement income, taxable benefits, marginal cost, roth conversion, Hold, 90T
- Source: 24/7 Wall St. — https://247wallst.com/personal-finance/social-security/2026/09/20/boomers-control-90-trillion-in-the-g-shaped-economy-at-70-the-safe-money-is-what-makes-his-social-security-taxable
- Author: Gerelyn Terzo
- Published: 2026-09-21T00:02:55+00:00
- Read time: 1 min
- Topics: boomers, social security, treasury yields, irs formula, combined income, g-shaped economy, retirement income, taxable benefits, marginal cost, roth conversion
## Social Security Tax Trap
Retirees earning 4% on $700,000 Treasuries see $14,700 of Social Security taxable at 70 due to 1984 IRS rules.

> The formula sits in a 1984 IRS rule that's never been updated since 1993.
## The G-Shaped Economy
Boomers control $90 trillion, or 52% of U.S. household wealth, including $3.1 trillion in money-market funds.
## Why Interest Taxes Benefits
Combined income formula adds half of Social Security to adjusted gross income, pushing retirees past $34,000 threshold.
## Taxable Impact
Each $1 in Treasury interest adds $1.85 to taxable Social Security, hitting 22.2% tax rate for retirees in 12% bracket.
## Roth Conversion Strategy
Spreading Roth conversions before RMDs reduces taxable Social Security by shifting income out of combined income formula.
## Tax Shelter Options
Municipal bonds and Roth IRAs avoid federal tax while still being counted in combined income calculations.
## The 1984 Formula
Congress wrote the Social Security tax formula in 1984 and last updated it in 1993, ignoring rising interest rates.
## Key takeaway

Higher Treasury yields push retirees into taxable Social Security brackets despite unchanged 1984 IRS thresholds.