Back Pay Tax Calculator

How is tax on back pay calculated in Australia?

Back pay is not taxed at its own rate. The ATO publishes Schedule 5 (NAT 3348) to spread the payment back across the pay periods it belongs to, so the tax comes out close to what you would have paid had the money arrived on time. The alternative, dropping the lump sum into one pay period, taxes it all at your top marginal slice for that period.

Which method applies turns on one question: does the back pay relate to the current financial year, or an earlier one?

Step by step, using the ATO's own example

1. Split the back payment by the year it relates to. Work out how much of the payment accrued in the current financial year and how much relates to an earlier one. Each part runs through a different method.
2. Apportion the current-year part across the periods it covers. In the ATO's own example, $800 of back pay covering 8 weekly periods is $100 a period.
3. Rework the tax for each of those periods. Add the $100 to the $1,600 originally paid, look up the tax on $1,700, and subtract the $331 already withheld. That leaves $32 a period.
4. Total the differences. Eight periods at $32 gives $256 withheld from the back payment.
5. Add the tax on this period’s normal pay. Tax on the current $1,700 is $363, so the payslip shows $619 withheld in total.

Which Schedule 5 method will my employer use?

There are three, and the ATO accepts any correctly applied one. That is why two employers can lawfully withhold different amounts from an identical back payment.

The gap is real but modest. On the ATO's published example, $800 of back pay covering 8 weekly periods on $1,600 a week, Method B(i) withholds $256 and Method A withholds $208. Whichever your employer used, the difference is settled when you lodge.

Why was so much tax taken out of my back pay?

Almost always because the lump sum was added to a single pay period and run through the regular tax table. The bigger the back payment relative to your normal pay, the more that costs you up front.

On $2,200 a week, a $12,000 back payment covering 26 weeks should have $3,952 withheld under Schedule 5. Lumped into one pay it takes $5,496, which is $1,544 more than the ATO method asks for.

For small back payments the two land within a few dollars of each other, and Schedule 5 can even take slightly more. It is the large payments where the method matters. Either way the excess is not lost: it returns as a refund when you lodge, because your real liability is worked out on the year's total income.

Prior-year arrears run through Method B(ii), which averages your earnings to date. On $2,400 a fortnight twelve periods into the year, $10,000 of arrears has $3,224 withheld against $4,114 if it were lumped in, a gap of $890.

How much tax is withheld on common back payment amounts?

Resident rates for 2026-27 with the tax-free threshold claimed and no study loan, calculated under Method B(i) for back pay relating to the current financial year.

What is Lump Sum E, and does it cut my tax?

Lump Sum E is a back payment of remuneration that accrued, or was payable, more than 12 months before it was paid. It appears as its own line on your income statement, broken down by the financial year each part relates to.

The $1,200 threshold is gone. Before 1 July 2025 a back payment was only reported as Lump Sum E if it reached $1,200. From 1 July 2025 that threshold no longer applies, so any qualifying amount is reported as Lump Sum E whatever its size.

Being reported as Lump Sum E does not by itself reduce your tax. What can is the lump sum payment in arrears tax offset, and it is gated on a threshold test: the arrears must be at least 10% of your taxable income once the arrears themselves, any net capital gains, employment termination payments, unused leave paid on termination and super lump sums are taken out. Clear that and the ATO compares the tax on the arrears now against what it would have cost in the years it accrued, and credits the difference.

The offset is often nil, because arrears frequently sit in the same bracket in both years. The ATO states it publishes no calculator for the offset and that the myTax estimate excludes it, so the figure only appears on your notice of assessment. Since 1 July 2024 a qualifying lump sum in arrears can also be excluded from your Medicare levy calculation.

Back pay, bonus or commission: what is the difference?

All three run through Schedule 5, but they are not the same thing and the ATO distinguishes them.

• Back pay is money that should have been paid earlier, usually an underpayment against an award or an allowance that was missed. A bonus counts as back pay only if it was paid later than it should have been.
• A bonus recognises performance or service and may not relate to a particular period. A sign-on bonus or a one-off payment for a changed work location is treated the same way. Work out that figure on the bonus tax calculator.
• A commission recognises performance or service, often as a percentage of a transaction. Run it through the commission tax calculator.

One important exclusion: if the payment relates to a single pay period, Schedule 5 does not apply at all. It is added to that period's earnings and the regular weekly tax table does the work. Working holiday makers are outside Schedule 5 entirely and use Schedule 15 for every payment.

Sources

• ATO: Schedule 5: Working out the withholding amount (NAT 3348, QC107123, published 17 June 2026). Method A, B(i), B(ii) and the 47% limit.
• ATO: Schedule 5: Withholding amounts examples. The four worked examples this page's engine is tested against.
• ATO: Lump sum payment in arrears (QC72204, updated 8 June 2026). The offset, the 10% threshold test and the Medicare levy exemption.
• ATO: Reporting back payments (QC66099, updated 16 July 2025). Lump Sum E and the removal of the $1,200 threshold.
• ATO: Schedule 1: Statement of formulas (NAT 1004). The tax table every step above looks up.