The belief that earning more can leave someone worse off after tax is remarkably persistent. It comes from misreading how a marginal rate applies, and the misreading has practical consequences.
Rates apply to slices, not to totals
A progressive system divides income into bands, each taxed at its own rate. Income falling in a band is taxed at that band's rate regardless of what happens above it.
Crossing a threshold therefore changes the rate on the amount above it only. Income already earned below the threshold continues to be taxed exactly as before.
The common misconception treats the highest applicable rate as though it applied to every unit of income, which would indeed create a cliff. The system is built specifically to avoid one.
Marginal and effective rates answer different questions
The marginal rate is the rate on the next unit earned, and it is the relevant figure for deciding whether additional work or a bonus is worthwhile.
The effective rate is total tax divided by total income, and it is always lower than the marginal rate in a progressive system because the lower bands pull it down.
Confusing them produces bad comparisons, particularly when people describe their tax burden using a band rate they only pay on a small slice of income.
Withdrawal of benefits creates the real cliffs
Genuine cliffs do exist, but they come from benefits, allowances and credits that phase out as income rises rather than from the rate bands.
Where a payment is withdrawn abruptly at a threshold rather than tapered, a small increase in income can reduce net resources. This is a feature of the benefit design, not the tax schedule.
Tapered withdrawals produce a similar but gentler effect, adding to the effective marginal rate over the phase-out range in a way the published bands do not show.
Payroll deduction can create a temporary illusion
Withholding systems estimate annual tax from the current pay period, so a one-off bonus can be treated as though it were the new normal.
The deduction taken looks disproportionate, which appears to confirm the misconception even though the annual calculation later corrects it.
The correction arrives at reconciliation, either through an adjustment in later pay or at filing, depending on how the system is administered locally.
Why the misconception matters
People decline overtime, promotions and additional hours on the basis of it, which is a real cost imposed by a misunderstanding.
Employers encounter the same reasoning during pay negotiations, where the perceived tax effect can outweigh the actual one.
Band structures, thresholds and phase-out rules differ substantially by jurisdiction and change over time, so the specific figures always need checking against current local rules.