Reference

Marginal and effective: the two rates that matter.

Marginal is what one extra euro is taxed at. Effective is what your income is taxed at on average. Both are correct; both are routinely confused; the difference shapes most personal financial decisions.

The two definitions

Marginal tax rate — the rate applied to the next euro of income. If you are currently earning €60,000 and a raise brings you to €60,500, the marginal rate is the percentage of that €500 that goes to tax. In Ireland 2025/26, the marginal rate is 40 % for income above €44,000, plus PRSI plus USC.
Effective tax rate — total tax divided by total gross income. Captures the average burden across your full salary.

The two diverge because progressive systems tax different slices of income at different rates. A worker on €60,000 in Ireland has €44,000 taxed at 20 % (with credits applied) and €16,000 taxed at 40 %. The marginal rate is 40 %; the effective rate is closer to 25 %.

Worked example: Irish PAYE worker, €60,000 gross

Slice of income	Rate	Tax in band
First €44,000	20%	€8,800
Next €16,000 (€44k–€60k)	40%	€6,400
Income tax subtotal		€15,200
Less: personal tax credit		(€2,000)
Net income tax		€13,200
PRSI 4.1% on full income	4.1%	€2,460
USC progressive (illustrative)		€1,930
Total tax + social charges		€17,590

Effective rate: 17,590 / 60,000 ≈ 29.3%. Marginal rate (the next euro): 40% income tax + 4.1% PRSI + 4% USC ≈ 48.1%. Same person, very different rates depending on the question being asked.

Which rate to use, by decision

How much tax am I paying overall? Effective rate.
Should I take this raise / bonus? Marginal rate. Always positive in nominal terms even at high marginal rates, because you keep (1 − marginal) of the extra euro.
Should I contribute to a pension? Marginal rate. Pension contributions reduce taxable income at the marginal rate; the savings are computed against the rate of the highest-taxed slice of your income.
How much do I need to gross to net €X? Marginal rate, applied as gross = net + (net × marginal / (1 − marginal)).
What's my purchasing power compared to last year? Effective rate (along with inflation).

The 'I don't want a raise because it pushes me into the higher bracket' fallacy

The fallacy: “Crossing into the higher bracket means all my income is now taxed at the higher rate, so I'll take home less.” Mathematically impossible under a marginal-rate system. A €1 raise that pushes you over a threshold is taxed at the higher marginal rate on that €1 only; income below the threshold remains at the lower rate. You always take home more after the raise — you just keep less of the marginal euro than you would have at the lower rate.

A handful of edge cases (the UK personal-allowance taper above £100,000, the Irish age-related exemption, certain US benefit cliffs) do produce genuine effective-marginal-rates greater than 100 % over narrow income ranges. They are exceptional and the calculator does not encounter them in normal use. The “I'll lose money by crossing the bracket” concern almost always reflects the fallacy, not these edge cases.

Where the calculator reports both

The main calculator reports effective rate and marginal rate as separate output items. The bracket-by-bracket breakdown shows exactly how much of your income falls into each band and how much tax accrues from each. Use the marginal figure when planning the next financial decision; use the effective figure when explaining your overall burden to a partner, accountant, or budget.