Step 1 · Provisional Income
Combined Income (Provisional Income)
PI = B + (A × 50%)
Provisional Income = Other Income + half of your Social Security benefit
Other income (B)$30,000
+ 50% of SS benefits$12,000
= Provisional Income (PI) $42,000
This is the key figure the IRS uses to determine how much of your Social Security is taxable.
Step 2 · First Threshold Test · $25,000 / $32,000
How Much Exceeds the Base Threshold?
Excess₁ = MAX(0, PI − T1)
How far does your Provisional Income exceed the base threshold? That excess is what starts to make SS taxable.
T1 threshold Single: $25k $25,000
Provisional Income (PI) $42,000
= Excess above T1 $17,000
Single filers: $25,000 · Married filing jointly: $32,000 · Married filing separately: $0
Step 3 · First Tier (up to 50% taxable)
Taxable Amount — Tier 1
Tier1 = MIN(Excess₁, A × 50%, (T2 − T1) / 2)
The first taxable chunk is the smallest of three limits: the excess from Step 2, half your SS benefit, or half the dollar band between the two thresholds — whichever is lowest wins.
Excess above T1$17,000
50% of SS benefits (A×50%)$12,000
½ of T1→T2 band$4,500
= Tier 1 taxable $4,500
MIN of three values: excess above T1, half your SS benefit, and half the band between T1 and T2.
Step 4 · Second Threshold Test · $34,000 / $44,000
How Much Exceeds the Upper Threshold?
Excess₂ = MAX(0, PI − T2)
Now check the upper threshold. Any Provisional Income beyond this point triggers the steeper 85% rate on the additional amount.
T2 threshold Single: $34k $34,000
Provisional Income (PI) $42,000
= Excess above T2 $8,000
Single: $34,000 · Married jointly: $44,000 · Married separately: $0. Above this, up to 85% of SS is taxable.
Step 5 · Second Tier (up to 85% taxable)
Taxable Amount — Tier 2
Tier2 = MIN(Excess₂ × 85%, A × 85% − Tier1)
85 cents of every dollar above the upper threshold is taxable — but the total can never push your taxable SS above 85% of your full benefit.
Excess above T2 × 85%$6,800
85% of SS − Tier1 (cap)$15,900
= Tier 2 taxable $6,800
85 cents of every dollar above T2 is taxable, up to 85% of total SS benefit.
Result · Taxable SS Amount
Total Taxable Social Security
Taxable SS = MIN(Tier1 + Tier2, A × 85%)
Add Tier 1 and Tier 2 together — then apply one final ceiling: no matter what, the taxable amount can never exceed 85% of your total Social Security benefit.
Tier 1 taxable$4,500
+ Tier 2 taxable$6,800
Subtotal$11,300
85% cap on SS benefit (max allowed)$20,400
Taxable Social Security
= X% of your benefit
$11,300
up to 50%
SS taxable
T1 ≤ PI < T2
up to 85%
SS taxable
PI ≥ T2