The tips and overtime deductions do not shrink smoothly. They shrink in steps, and the step is $100. Schedule 1-A takes the amount by which your income exceeds the threshold, divides it by $1,000, and — in the form's own words — instructs you to "decrease the result to the next lower whole number." That whole number is multiplied by $100 and taken off your ceiling.

Rounding down is the detail worth understanding. It means income between the steps is free, and income that crosses a step costs $100 of deduction all at once.

How the step works

Take a single filer, whose threshold for both deductions is $150,000.

MAGI $153,900 — three full thousands of excess

  1. Line 1Excess over $150,000$3,900
  2. Line 2Divided by $1,0003.9
  3. Line 3Decreased to the next lower whole number3
  4. Line 4Reduction (3 × $100)−$300

MAGI $154,000 — one hundred dollars more income

  1. Line 1Excess over $150,000$4,000
  2. Line 2Divided by $1,0004.0
  3. Line 3Decreased to the next lower whole number4
  4. Line 4Reduction (4 × $100)−$400

$100 more income cost $100 of deduction. Everything between $153,000 and $153,999 produced the same $300 reduction — that whole band was free.

Where the steps fall

The boundaries sit at exact thousands above the threshold. For a single filer that is $151,000, $152,000, $153,000 and so on. For joint filers the same pattern starts from $300,000.

So the useful question is not "how close am I to the threshold" but "where am I within the current thousand." Someone at $153,950 is $50 away from losing another $100 of deduction. Someone at $153,050 has $950 of headroom.

How much a step actually costs

A $100 reduction in the deduction is not $100 out of your pocket. It is $100 of income that becomes taxable again, so the cost is $100 multiplied by your marginal rate.

Crossing one boundary — what it costs

  1. Line 1Deduction lost$100
  2. Line 2Extra tax at a 12% marginal rate$12
  3. Line 3Extra tax at a 22% marginal rate$22

That is the honest size of this cliff. It is worth knowing about and it is not worth turning down a shift over. The reason to understand the mechanic is that it tells you when small income changes matter and when they do not — and for these two deductions, the answer is usually they do not.

Contrast that with the senior deduction, which reduces by a straight 6% of the excess with no rounding at all. There, every dollar moves the number, and the cost per dollar is six times higher than the average cost per dollar here.

Where the deduction runs out entirely

The steps eventually consume the whole ceiling. This point is not printed as a headline figure anywhere, but it follows directly from the method, so you can check the arithmetic yourself.

Tips — single filer, $25,000 ceiling

  1. Line 1Ceiling ÷ $100 per step250 steps
  2. Line 2Excess income needed (250 × $1,000)$250,000
  3. Line 3Threshold$150,000
  4. Line 4Deduction reaches zero at$400,000

Overtime — single filer, $12,500 ceiling

  1. Line 1Ceiling ÷ $100 per step125 steps
  2. Line 2Excess income needed (125 × $1,000)$125,000
  3. Line 3Threshold$150,000
  4. Line 4Deduction reaches zero at$275,000

For joint filers, both ceilings are consumed over $250,000 of excess — tips because the ceiling stays at $25,000, overtime because it doubles to $25,000 — so both reach zero at $550,000 of MAGI.

Note the asymmetry that produces. A single filer loses the overtime deduction at $275,000 while the tips deduction still has more than half its value left. Someone with both kinds of income watches them disappear at different rates from the same rising MAGI.

Quick answers

  • Is the reduction taken from my ceiling or my tips? From the ceiling. If your qualified tips are below the reduced ceiling, the phase-out has not cost you anything — you were never using the full amount.
  • Does the same rounding apply to the senior deduction? No. That one is a flat 6% of the excess with no rounding. Two different mechanics on the same form.
  • Should I try to land just under a boundary? The arithmetic says the gain is $12 to $22. Deliberately reducing income to capture that is almost never worth it. Pre-tax retirement or HSA contributions, which reduce MAGI for other reasons anyway, are a different matter.
  • Which income figure sets the excess? The MAGI computed in Part I of Schedule 1-A, not the AGI on your 1040. See our guide to MAGI.

The overtime calculator and tips calculator apply the rounding exactly as the form does, so you can see which step your income lands on rather than estimating it.