Social Security tax torpedo
In a certain income band, each extra dollar a retiree takes — an IRA withdrawal, a Roth conversion — drags up to 85¢ of Social Security into taxable income, spiking the effective marginal rate far above the stated bracket. Surface it before they pull the trigger.
1 · Make the call
Send the benefits, other income, and the client's ordinary bracket to
/v1/tax/social-security-benefits.
curl -X POST https://api.numeratica.com/v1/tax/social-security-benefits \
-H "Authorization: Bearer nmr_sk_test_xxx" \
-H "Content-Type: application/json" \
-d '{
"filing_status": "single",
"social_security_benefits": 24000,
"other_income": 35000,
"marginal_ordinary_rate": 0.22
}'2 · The response
The §86 worksheet result, plus the two numbers that matter for planning:
marginal_inclusion_rate (how much SS the next dollar pulls in) and
effective_marginal_rate (the real cost of that dollar).
{
"result_id": "sstax_7f2775b14ec0078b",
"engine_version": "ss-tax-1.0.0",
"result": {
"provisional_income": 47000,
"taxable_social_security": 15550,
"taxable_percent": 0.6479,
"tier": 2,
"marginal_inclusion_rate": 0.85,
"effective_marginal_rate": 0.407
},
"disclaimer": "Calculation engine output for informational purposes only; not financial or tax advice."
}At $35k of other income this client sits in the 85% phase-in: the next $1 of ordinary income
pulls $0.85 of benefits into tax, so a 22% bracket behaves like 40.7%. Push
other income to $45k and benefits are already 85%-taxed (the max) — the inclusion rate drops to
0 and the marginal rate falls back to 22% (result_id
sstax_071d2c5894961b19). That hump in between is the torpedo.
3 · Render it
Turn it into a warning card an advisor can drop into a client review.
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<div style="background:#fffbeb;padding:16px 20px;border-bottom:1px solid #e6e9ef">
<span style="display:inline-block;background:#b45309;color:#fff;font-size:12px;font-weight:700;padding:3px 11px;border-radius:999px;letter-spacing:.04em">⚠ TAX TORPEDO</span>
<div style="color:#5b6675;font-size:13px;margin-top:12px">Effective rate on the next $1 of income</div>
<div style="font-size:34px;font-weight:700;color:#b45309;line-height:1.1">40.7%</div>
<div style="color:#9aa3b0;font-size:12px">stated bracket is just 22%</div>
</div>
<div style="padding:8px 20px 14px;font-size:14px">
<div style="display:flex;justify-content:space-between;padding:7px 0;border-bottom:1px solid #f1f3f7"><span style="color:#5b6675">Provisional income</span><strong>$47,000</strong></div>
<div style="display:flex;justify-content:space-between;padding:7px 0;border-bottom:1px solid #f1f3f7"><span style="color:#5b6675">Taxable Social Security</span><strong>$15,550 (64.8%)</strong></div>
<div style="display:flex;justify-content:space-between;padding:7px 0;border-bottom:1px solid #f1f3f7"><span style="color:#5b6675">Phase-in tier</span><strong>Tier 2 · 85% band</strong></div>
<div style="display:flex;justify-content:space-between;padding:7px 0"><span style="color:#5b6675">Each $1 more income →</span><strong>+$0.85 taxable SS</strong></div>
</div>
<div style="padding:10px 20px;color:#5b6675;font-size:12px;border-top:1px solid #f1f3f7">Single · $24k SS + $35k other income · result_id sstax_7f2775b14ec0078b · not tax advice</div>
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