Backpay Calculator Australia
Work out the gross backpay you are owed from an underpayment, and how the lump sum is withheld under ATO Schedule 5 for 2026-27.
Backpay Calculator 2026-27
How is backpay calculated?
Two numbers, multiplied. The work is in getting each one right.
Backpay is the weekly shortfall multiplied by the number of weeks it ran. Underpaid $50 a week for 26 weeks, you are owed $1,300 before tax. The shortfall is the gap between what you were paid and what your award, agreement or contract required for the same hours.
The reference rates for 2026-27 come from the Fair Work Commission’s Annual Wage Review 2026 decision ([2026] FWCFB 3500). From the first full pay period starting on or after 1 July 2026, the National Minimum Wage is $26.44 per hour, or $1,004.90 for a 38-hour week. Minimum award wages rose 4.75% at the same time. Most employees are covered by an award, so the award minimum, not the flat National Minimum Wage, is usually the rate to check.
Casuals have one extra step. A casual employee is generally owed a 25% loading on top of the base hourly rate, per Fair Work’s casual employment guidance. Paid the permanent rate while employed as a casual, your weekly shortfall is the missing loading on every hour worked. The casual loading calculator works that rate out for you.
Fair Work’s Pay and Conditions Tool and its downloadable pay guides carry the exact 1 July 2026 minimum for each award classification. Compare that rate with your payslip rate, and the weekly gap times the affected weeks is your gross backpay figure for the calculator above.
How much backpay at common underpayment amounts?
Gross backpay owed, before tax, at common weekly shortfalls.
| Underpaid per week | 4 weeks | 13 weeks | 26 weeks | 52 weeks |
|---|---|---|---|---|
| $25 | $100 | $325 | $650 | $1,300 |
| $50 | $200 | $650 | $1,300 | $2,600 |
| $75 | $300 | $975 | $1,950 | $3,900 |
| $100 | $400 | $1,300 | $2,600 | $5,200 |
| $150 | $600 | $1,950 | $3,900 | $7,800 |
| $200 | $800 | $2,600 | $5,200 | $10,400 |
Gross amounts, before PAYG withholding. 13 weeks is one quarter, 26 weeks is half a year of underpayment. Computed from the weekly shortfall times the number of weeks.
How is tax withheld from a backpay lump sum?
ATO Schedule 5 (NAT 3348) governs back payments, and the method depends on when the underpayment happened.
A backpay lump sum lands in one pay run, but it belongs to many. If your employer withheld tax on it as if it were one week’s pay, far too much would come out. So the ATO publishes Schedule 5, the tax table for back payments, commissions, bonuses and similar payments, published 17 June 2026 and applying to payments made from 1 July 2026.
One scope rule comes first. If the payment relates to a single pay period, Schedule 5 does not apply at all. It is added to your other earnings for that period and withheld under the regular tax table. Schedule 5 only applies when the payment covers more than one pay period, or an undefined period, which is what backpay almost always does.
| Situation | Schedule 5 method | 47% cap on withholding? |
|---|---|---|
| Payment relates to a single pay period | None. Regular tax table applies | Not relevant |
| Backpay to specific periods in the current financial year | Method B(i), recalculates each affected period | No cap |
| Backpay for a prior financial year | Method B(ii), spread over the whole year | Capped at 47% |
| Any additional payment, simplest option | Method A, apportioned over the year | Capped at 47% |
Source: ATO Schedule 5 (NAT 3348, QC107123), published 17 June 2026. Employers may use Method A or Method B; both are acceptable to the ATO. If a calculation returns a negative amount, the result is treated as nil.
What happens with backpay for the current financial year?
Method B(i) rebuilds each pay period as if you had been paid correctly.
Backpay for pay periods in the current financial year is withheld under Schedule 5 Method B(i). It is the most accurate method, because it does not estimate. It goes back to each affected pay period and asks what the withholding would have been if the right amount had been paid.
| Step | What the employer does |
|---|---|
| 1 | Work out how much of the back payment applies to each earlier pay period in the current financial year. |
| 2 | For the first affected period, add that portion to the normal earnings previously paid. |
| 3 | Work out the withholding on that total from the relevant tax table. |
| 4 | Subtract the amount previously withheld for that period. |
| 5 | Repeat steps 2 to 4 for each affected period, and total the step 4 amounts. |
| 6 | Work out the withholding on current-period gross earnings, excluding the backpay. |
| 7 | Total PAYG for the pay run is step 5 plus step 6. |
Schedule 5 Method B(i), ATO NAT 3348. No 47% cap applies to Method B(i).
The result matters to you for one reason. Because each period is recalculated at the rate that should have applied, the withholding tracks the tax you actually owe far more closely than a flat rate would. The lump sum is not punished for arriving late.
What about backpay for a previous financial year?
Method B(ii) spreads the payment over the year, and a 47% ceiling applies.
Backpay that relates to a prior financial year cannot be rebuilt period by period in the current year, so Schedule 5 uses Method B(ii). Your employer averages your earnings for the year to date, adds a per-period slice of the backpay on top, works out the extra withholding on that slice, and multiplies it back out across the pay periods in the year.
Withholding on the payment is then capped at 47% of the payment. On a $1,300 prior-year backpay, the most your employer can withhold from it under Method A or B(ii) is $611. The cap applies to the additional payment only, not to your normal earnings in the same pay run. If you see close to 47% come out, the cap has bound, and the excess above your real marginal rate comes back at tax time.
Three side rules from Schedule 5 are worth knowing. A back payment spanning two financial years is apportioned between them, with the applicable method applied to each part. Additional payments already made earlier in the year are not recalculated. And periods of leave without pay do not change the divisor; the payment is still spread over the full 52 weekly, 26 fortnightly or 12 monthly periods.
If you have a HECS-HELP or other study loan debt, the loan component is calculated using the same method, and combined with the tax component before the 47% cap is tested. The cap is one ceiling for both amounts together.
Is the tax withheld from backpay the tax you actually owe?
No. Schedule 5 is a withholding schedule, and withholding is an estimate.
Everything above describes withholding, the amount your employer holds back on payday. Your actual tax is calculated once, when you lodge your return, on your whole-year income at the 2026-27 rates. The withholding is credited against that bill. More withheld than owed, you get a refund. Less, you get a bill.
Put numbers on it. A $1,300 backpay on a $75,000 salary adds $416 to your actual 2026-27 tax, an effective 32% on the backpay, because it all sits in the 30% bracket plus the 2% Medicare levy. If your employer withheld more than that under Schedule 5, the difference is not lost. It comes back through your assessment, usually as a larger refund.
This is the same mechanism that makes bonus withholding look inflated, and it resolves the same way. The tax refund calculator estimates where your whole year lands once the backpay is included.
Backpay vs bonus: what is the difference?
Both run through Schedule 5. The method, and the cap, can differ.
| Backpay | Bonus or commission | |
|---|---|---|
| What it is | Wages you should have been paid in earlier pay periods | An additional payment for performance or sales |
| Single pay period | Rare, but if so the regular tax table applies | Common; added to that period’s pay, regular table applies |
| Multi-period, current year | Method B(i), recalculated per period, no cap | Method A, or B(ii), spread across the year |
| Prior financial year | Method B(ii) or A, 47% cap applies | Method B(ii) or A, 47% cap applies |
| Final tax | Settled at assessment, marginal rates | Settled at assessment, marginal rates |
Source: ATO Schedule 5 (NAT 3348). Method A carries an optional refinement: a payment covering a defined period under 12 months can be divided by the periods it actually relates to, rather than the full year.
The practical difference is Method B(i). It exists for back payments tied to specific current-year periods, and it is why well-handled backpay withholding lands close to the truth while bonus withholding often overshoots. If your payment is a bonus rather than backpay, the bonus tax calculator is built for it.
Who uses this backpay calculator?
Four situations account for most backpay searches.
The award worker after 1 July
Minimum award wages rose 4.75% from the first full pay period on or after 1 July 2026. An employer still paying the old rate is underpaying from that date, and the weekly gap times the weeks since is the backpay owed.
The casual missing the loading
Employed as a casual but paid the permanent base rate. The standard 25% casual loading on every hour worked is the shortfall, and it compounds quickly across a semester or a season of shifts.
The backdated pay rise
A rise agreed from 1 July but processed in October arrives as one lump sum. It is backpay to specific current-year periods, so Method B(i) applies and the withholding is recalculated per period.
The backdated agreement increase
A new enterprise agreement applies increases retrospectively, sometimes across two financial years. The payment is apportioned between years, and each part is withheld under its own Schedule 5 method.
What changed on 1 July 2026?
Three moves matter for backpay this year.
First, the rates that define underpayment moved. The National Minimum Wage rose to $26.44 per hour ($1,004.90 per week) and minimum award wages rose 4.75%, both from the first full pay period starting on or after 1 July 2026. Every rate rise creates a fresh window for underpayment where old rates keep being paid, which is why backpay searches spike after 1 July.
Second, the withholding tables changed underneath Schedule 5. The first marginal tax rate fell from 16% to 15%, and the ATO reissued all 15 withholding schedules and 12 tax tables from 1 July 2026. Schedule 5 itself was published on 17 June 2026 and applies to payments made from 1 July 2026, so the current document is confirmed for 2026-27, not carried forward.
Third, timing. The increase applies from the first full pay period on or after 1 July, not 1 July itself. In Fair Work’s worked example, a weekly period starting Monday means the new rate starts Monday 6 July 2026. That rule decides which weeks count when you count your underpaid weeks.
What are the common backpay mistakes?
Five errors cover most of the confusion.
Treating withholding as the final tax
Schedule 5 sets the payday estimate, nothing more. Your actual tax on backpay is your marginal rate at assessment, and over-withholding comes back as a refund.
Believing in a flat backpay tax rate
There is no special rate for backpay. The 47% figure is a withholding ceiling under Methods A and B(ii), not a rate anyone is meant to finally pay on it.
Applying the 47% cap to Method B(i)
Current-year backpay recalculated per period has no cap, and needs none, because the recalculation already lands near the true tax.
Counting weeks from 1 July
New minimum rates start at the first full pay period on or after 1 July 2026. Counting from 1 July itself can overstate the claim by up to a week.
Measuring the gap in take-home pay
Underpayment is measured in gross wages against the award rate. Comparing net amounts mixes tax into a Fair Work question and understates the shortfall.
Backpay FAQ
Common questions about backpay and how it is taxed.
Sources
The documents behind every figure on this page.
- ATO, Schedule 5: Tax table for back payments, commissions, bonuses and similar payments (NAT 3348, QC107123), published 17 June 2026, applies to payments made from 1 July 2026.
- ATO, Tax tables overview: 15 withholding schedules and 12 tax tables updated from 1 July 2026.
- Fair Work Commission, Annual Wage Review 2026 decision ([2026] FWCFB 3500), announced 2 June 2026.
- Fair Work Ombudsman, Minimum wages and Minimum wages increase from 1 July 2026, both updated 1 July 2026.
- Fair Work Ombudsman, casual employment guidance on the 25% casual loading.
Last verified 23 July 2026.
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