How marginal tax actually works, and why your bonus isn't all taxed at 45%

A bonus lands, you check your payslip, and a large chunk of it is gone. The instinct is to conclude that a bonus gets taxed at some brutal flat rate, so it is barely worth having. That instinct is wrong. The gap between what people believe here and what actually happens is one of the most common misunderstandings in South African personal finance. This is a short, factual companion to our marginal and capital gains tax calculator, and its only job is to show you how the brackets really work. It is general information about the mechanics, not advice about your own return.

Everything here is South Africa specific, built on the SARS tax tables for the 2027 year of assessment, which runs from 1 March 2026 to 28 February 2027.[1]

Income is taxed in slices, not in one lump

South Africa uses a sliding scale of tax brackets.[1] Your income is not taxed at a single rate. It is cut into slices, and each slice is taxed at its own rate. For the 2027 tax year the brackets for individuals run like this: the first R237,100 and a bit is taxed at 18%, the next slice at 26%, then 31%, 36%, 39%, 41%, and only income above R1,878,600 is taxed at the top rate of 45%.[1] After the tax is worked out, a rebate is subtracted, which is why the lowest earners pay nothing at all.

The word that matters here is marginal. Your marginal rate is the rate on your next rand, the bracket your income currently sits in. It is not the rate you pay on everything you earn. That distinction is the whole article, and it is where the bonus myth comes from.

Why the bonus isn't all taxed at the top rate

Because income is taxed in slices, extra income is only taxed in the slice it lands in. The correct way to work out the tax on a bonus is the aggregation method: you calculate the tax on your income with the bonus, then subtract the tax on your income without it. The difference is the tax on the bonus.[2] Nothing else in your income is affected.

Take a worked example we use across this cluster. Thandi earns a taxable R520,000 and receives a R38,000 bonus.[3] Her income of R520,000 sits inside the 31% bracket. Add the R38,000 and her income becomes R558,000, which crosses into the 36% bracket at R530,200. So the bonus is taxed in two pieces: about R10,200 of it fills the rest of the 31% bracket, and the remaining R27,800 falls into the 36% bracket. The tax on the whole bonus works out to about R13,170, an average of 34.7% on the R38,000.[3]

Notice what did not happen. None of the bonus was taxed at 45%, because her income never reached the top bracket. And the tax on her original R520,000 did not change at all. A bonus cannot push your existing income into a higher bracket.

It only taxes the new money, slice by slice.

Marginal versus effective: two rates, both true

Once the slicing is clear, a second number falls out of it, and confusing the two is the other half of the misunderstanding.

Your marginal rate is the rate on your next rand. In Thandi's case, after the bonus, that is 36%. Your effective rate is the total tax you pay divided by your total income. Thandi's total tax on R558,000, after the rebate, is about R117,787, which is an effective rate of roughly 21%.[3] Both numbers are correct. They just answer different questions. The marginal rate tells you what an extra rand of income will cost you. The effective rate tells you what your income costs you on average.

People quote the marginal rate ("I'm in the 41% bracket") as though it were the effective one, and then conclude they lose 41% of everything. They do not. The effective rate is always lower, because the earlier slices were taxed in lower brackets and the rebate reduces the tax at the bottom. The two only converge for someone earning far into the top bracket, and even then the rebate keeps them slightly apart.

Where this actually matters

The mechanics are not just trivia. They change how you read three common situations.

A raise is never eaten by "moving into a higher bracket". Only the part of the raise that crosses into the new bracket is taxed at the higher rate. Turning down income to "avoid a bracket" is based on a myth: you are always better off with the extra rand, because only that rand, and only the part of it above the threshold, is taxed more.

A bonus looks worse on the payslip than it is at assessment. Employers work out the pay-as-you-earn on a bonus month by annualising it, which often over-withholds, and the difference comes back when your return is assessed. The tax you actually owe on the bonus is the aggregation figure above, not the amount that came off in that one month.

Additional income, from a side arrangement, freelance work, or interest, is taxed at your marginal rate, because it stacks on top of your existing income. Knowing your marginal rate tells you what you keep from the next rand, which is the number that matters when you are weighing whether extra income is worth the effort.

The one idea to keep

South African income tax is a staircase, not a cliff. Each slice of your income is taxed at its own rate, a bonus is only taxed in the slice it lands in, and your marginal rate is the rate on your next rand, not the rate on everything you earn. Once you can see the staircase, the payslip stops being alarming and starts being predictable. If you want to see the exact figure on a specific bonus, raise, or piece of extra income, our marginal and capital gains tax calculator does the aggregation for you, for the tax year you choose. The figures here are the current SARS tables and are refreshed each year after the February Budget.