How Bunnings Underpaid Workers' Superannuation for a Decade: Technical Breakdown
Small per-employee errors create large aggregate liabilities. $95 per worker times 40,000 workers equals $3.8 million. Do not dismiss small errors.
The Bunnings superannuation underpayment is, on the surface, one of the smaller scandals -- $3.8 million across 40,000 workers averages just $95.33 per person. But the case is important for what it reveals about how payroll system errors can persist for years without detection, and how even a small per-employee error creates a massive aggregate liability when multiplied across a large workforce.
A coding error in Bunnings' payroll system failed to correctly calculate superannuation contributions for part-time employees who worked beyond their annual contracted hours. This single bug, running silently for nearly a decade, affected 40,000 workers.
What Happened
Bunnings, Australia's largest hardware retail chain and a subsidiary of Wesfarmers, identified that part-time workers had been underpaid superannuation entitlements due to a coding error in its payroll system.
Timeline
- ~2010-2019: Payroll coding error silently underpaid superannuation for part-time staff
- 2019: Error identified and disclosed
- 2019: Bunnings committed to repaying $3.8 million to 40,000 current and former workers
- 2019: Average compensation of $95.33 per affected worker
The Numbers
| Metric | Detail |
|---|---|
| Workers affected | 40,000 current and former employees |
| Total underpayment | $3.8 million |
| Average per worker | $95.33 |
| Period | Nearly 10 years |
| Root cause | Payroll system coding error |
| Type of underpayment | Superannuation (super guarantee) |
| Employment type affected | Part-time workers |
The Technical Failure
Superannuation errors are invisible to workers. Unlike wages, super is not received directly by employees. Compliance verification must be employer-driven because workers cannot easily verify their own entitlements.
The Superannuation Guarantee
Under Australian law, employers must pay a minimum percentage of an employee's ordinary time earnings (OTE) into a superannuation fund. The current rate is 12% (as of 2025-26). This applies to all employees earning more than $450 per month (threshold removed from 1 July 2022).
For part-time employees, superannuation must be calculated on all ordinary time earnings, including:
- Regular rostered hours
- Additional hours worked up to the full-time equivalent (before overtime kicks in)
- Leave payments
- Certain allowances
What the Coding Error Did
Bunnings' payroll system had a bug in how it calculated superannuation for part-time employees who worked additional hours beyond their contracted pattern. Specifically:
Part-time employees who picked up extra shifts (but not overtime shifts) should have had superannuation calculated on those additional ordinary-time hours. The payroll system's code did not include these additional hours in the superannuation calculation.
Example:
A part-time employee contracted for 20 hours/week who works 30 hours in a given week:
- Hours 1-20: Contracted hours (super correctly calculated)
- Hours 21-30: Additional ordinary hours (super should be calculated but was NOT)
- Hours 31+: Overtime (super not required on overtime)
The payroll system treated hours 21-30 the same as overtime, excluding them from the super calculation. This was wrong -- these were additional ordinary hours, not overtime, and should have attracted superannuation contributions.
Why the Error Persisted for 10 Years
This type of error is particularly insidious because:
It is invisible on individual pay slips. Superannuation is paid to a fund, not to the employee directly. Workers do not typically check their super fund balance against what should have been contributed.
The per-period error is tiny. For a worker who occasionally picks up an extra 5 hours, the super shortfall might be $5-10 per pay period. Nobody notices.
It only affects a subset of workers. Part-time employees who only work their contracted hours are unaffected. The error only triggers when additional hours are worked -- making it intermittent and harder to detect.
Payroll system testing rarely covers edge cases. The main scenarios (contracted hours, overtime) were presumably tested correctly. The edge case of additional ordinary hours for part-timers was missed.
Super guarantee audits focus on totals, not calculations. Standard audit procedures often verify that super was paid but may not re-derive the calculation from source data to verify it was calculated correctly.
The silent error -- $95 per employee. Invisible on pay slips. Intermittent in occurrence. Buried in a payroll system's code. And it ran for a decade, affecting 40,000 workers. This is the type of error that only automated, independent compliance verification can catch.
How It Could Have Been Detected Earlier
Independently calculate ordinary time earnings from timesheet data and compare against the payroll system's OTE figure. This catches coding errors that exclude certain hour types from super calculations.
Independent Super Guarantee Verification
Independent calculation of OTE: A compliance tool that independently calculates ordinary time earnings from timesheet data and compares the result against the payroll system's OTE figure would have identified the discrepancy for part-time workers with additional hours.
Super contribution reconciliation: Comparing the super actually paid (as reported to super funds) against an independently calculated obligation would have revealed the shortfall.
Part-time hours analysis: Automated identification of part-time workers regularly working above contracted hours, with verification that super is calculated on all ordinary hours (not just contracted hours).
Payroll system regression testing: After any payroll system update, running a comprehensive set of test cases that include part-time additional hours scenarios would have caught the bug if it was introduced by a software update.
How AirComply Prevents This
Independent Entitlement Calculation
AirComply calculates all entitlements -- including superannuation obligations -- independently of the payroll system. By comparing AirComply's calculation against what the payroll system actually contributes, discrepancies are identified regardless of their source.
Superannuation Compliance Monitoring
AirComply specifically tracks super guarantee obligations by:
- Calculating ordinary time earnings from actual hours worked
- Correctly classifying hours as ordinary vs overtime
- Applying the current super guarantee rate
- Comparing calculated obligations against actual contributions
Part-Time Employee Monitoring
AirComply monitors part-time employees' actual hours against contracted hours and ensures that all additional ordinary hours receive correct treatment -- including superannuation calculations. The system flags when part-time employees regularly work above their contracted hours, which triggers both super compliance checks and potential casual conversion obligations.
Edge Case Coverage
AirComply is designed to handle the edge cases that payroll systems often miss:
- Part-time additional hours (not overtime, not contracted)
- Split shifts that cross penalty rate boundaries
- Public holidays falling on regular working days for part-timers
- Leave accrual on additional hours
After any payroll system update, run regression testing that includes edge cases like part-time additional hours scenarios. The Bunnings bug may have been introduced by a software update and never caught.
Key Takeaways
Coding errors can persist for years. Software bugs do not fix themselves. Without independent verification, a single coding error can run for a decade.
Small per-employee errors create large aggregate liabilities. $95 per worker times 40,000 workers equals $3.8 million. Do not dismiss small errors.
Superannuation errors are invisible to workers. Unlike wages, super is not received directly by employees. Compliance verification must be employer-driven because workers cannot easily verify their own entitlements.
Coding errors can persist for years. Software bugs do not fix themselves. Without independent verification, a single coding error can run for a decade.
Part-time workers face unique compliance risks. The interaction between contracted hours, additional ordinary hours, and overtime creates complexity that payroll systems frequently mishandle.
Wesfarmers' broader problem. Bunnings' $3.8 million super error is part of Wesfarmers' broader $24 million payroll problem (including Target's $9 million). When the same payroll infrastructure serves multiple brands, errors propagate across the group.
The bottom line -- A single line of code in Bunnings' payroll system excluded additional ordinary hours from superannuation calculations for part-time workers. Nobody noticed for 10 years. The error was silent, intermittent, and invisible on individual pay slips. The only way to catch errors like this is independent, automated verification that re-derives every calculation from source data. If you trust your payroll system to check itself, you are trusting the bug to find itself.
AirComply independently verifies superannuation obligations and all award entitlements. Check your compliance now.