Most investment returns are uncertain. Salary sacrifice offers one that is written into legislation: money routed into super before tax is taxed at a flat 15% instead of your marginal rate. For a middle-income earner that's an instant 17-point saving; for a top-bracket earner it's 30 points. No market movement required — the return arrives at the moment of contribution.
The trade is equally clear-cut: the money is locked away until preservation age (60 for anyone born after mid-1964). Everything about doing this well comes down to sizing that trade correctly.
The mechanics, with numbers
Say you earn $100,000 and sacrifice $10,000 into super in 2026–27:
- Without sacrifice: the $10,000 is taxed at your marginal 32% (30% + Medicare levy). You keep $6,800 in hand.
- With sacrifice: the $10,000 enters your fund, which pays 15% contributions tax. $8,500 lands in super.
You've turned $6,800 of spendable money into $8,500 of retirement money — a 25% uplift before the money earns anything. The same $10,000 sacrificed by someone on $200,000 (47% marginal) turns $5,300 into $8,500: a 60% uplift. The higher your bracket, the more violent the arbitrage. Run your own salary through the salary sacrifice calculator to see the exact take-home cost and super gain.
Two side effects worth knowing: sacrificing reduces your income tax but does not reduce HECS/HELP repayment income (reportable super contributions are added back), and your employer's 12% super guarantee must by law be calculated on your pre-sacrifice salary.
The cap: $30,000, shared with your employer
All concessional (before-tax) contributions — the 12% super guarantee plus your sacrifice — share one annual cap of $30,000. On $100,000, your employer already contributes $12,000, leaving $18,000 of cap space. On $200,000, the SG takes $24,000 and leaves only $6,000. High earners hit the ceiling much sooner than they expect; check the SG number before setting the sacrifice amount, because excess contributions are taxed back at your marginal rate plus an interest charge — unwinding the entire benefit.
Carry-forward is the power move. If your total super balance was under $500,000 at the previous 30 June, unused cap space from the past five financial years carries forward. Someone who contributed only the SG for years can have $50,000+ of accumulated space — usable in one hit. This is exceptionally valuable in a year with a capital gain, a redundancy payout, or a bonus: a large carry-forward contribution can neutralise the tax spike at exactly the moment your marginal rate peaks.
Who should think twice
Anyone who may need the money before 60. The lock-up is absolute outside severe hardship provisions. Money for a house deposit, a career break or a renovation doesn't belong here — with one exception below.
Low-income earners. At a 15–16% marginal rate the arbitrage is nearly zero (and below $18,200 it's negative). The better lever at low incomes is the government co-contribution: after-tax contributions attract up to $500 of free money — see the co-contribution calculator.
Very high earners at the Division 293 line. Above $250,000 of combined income and concessional contributions, an extra 15% tax applies to contributions — the arbitrage narrows from 32 points to 17. Still positive, but recalculate before assuming.
Anyone with expensive debt. Credit cards at 20% beat any super arbitrage. Clear those first.
The first-home exception
The First Home Super Saver scheme lets you withdraw voluntary contributions (up to $15,000 per year, $50,000 total) plus deemed earnings to buy a first home. It effectively lets first home buyers run the salary-sacrifice arbitrage on their deposit — saving inside super at 15% tax instead of outside at their marginal rate — without the until-60 lock-up. The uplift compounds meaningfully over a 3–5 year deposit timeline; model it with the FHSS calculator.
Sizing it in practice
A sensible default sequence for surplus income: clear high-interest debt → build the emergency buffer (offset if you have a mortgage) → then salary sacrifice, sized to stay under the cap and scaled to your bracket. Even $100 a fortnight, started at 35, compounds into six figures of extra balance by 60 — the super projection calculator makes the long-run effect concrete.
The arbitrage is guaranteed. The only real question is how much of your money you're willing to make patient.
Figures use 2026–27 settings: 12% super guarantee, $30,000 concessional cap, $500,000 carry-forward balance threshold, Division 293 at $250,000. General information, not financial advice.