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How Does the Building Cost Index Affect My Depreciation?

Published 26 June 2026 · Last updated 26 June 2026

Quick Answer

The Building Cost Index (BCI) reflects changes in construction costs over time. It affects depreciation by influencing the replacement cost of assets, which in turn impacts the capital works deductions under **Division 43**. Understanding BCI helps investors optimise their depreciation claims by accurately valuing their property's structural components.

The Building Cost Index (BCI) is a crucial tool for investors looking to understand how changes in construction costs impact their property depreciation claims. It reflects the fluctuation in costs associated with building materials and labour over time, which directly affects the valuation of a property's structural components under Division 43 of the Income Tax Assessment Act 1997.

Under Division 43, investors can claim deductions for capital works, which include the structural elements of a building such as walls, roofs, and floors. These deductions are based on the construction costs at the time the property was built. However, the BCI can cause these costs to vary, especially for properties constructed over different periods or in different market conditions.

The most common misconception investors have is that the BCI only affects new constructions. In reality, it also impacts the depreciation schedules of older properties, as the replacement cost must be adjusted to reflect current market conditions. If the BCI rises, it indicates an increase in construction costs, potentially leading to higher capital works deductions.

To see how this plays out, consider a 2010-built three-bedroom house in Sydney, purchased by an investor for $850,000. If the BCI indicates a 10% increase in construction costs since the property was built, the replacement cost for the building's structure would need to be adjusted accordingly. This adjustment can enhance the annual capital works deduction, leading to a more substantial tax benefit. For example, if the original deduction was $5,000 per year, a 10% increase due to BCI adjustments could raise this to $5,500, saving the investor an additional $185 annually at a 37% marginal tax rate.

In our experience reviewing thousands of properties across Australia, many investors overlook the impact of the BCI on their depreciation schedules. This oversight often results in under-claimed deductions, leaving money on the table. We frequently see investors misunderstanding how the BCI applies to both residential and commercial properties, missing opportunities to adjust their claims accordingly. Additionally, some investors fail to update their depreciation schedules when significant changes in the BCI occur, which can lead to outdated and less effective tax strategies.

The answer can differ depending on your situation. For instance, if you acquired a second-hand residential property after 9 May 2017, the rules regarding plant and equipment depreciation under Division 40 changed significantly. However, the BCI primarily affects Division 43 capital works deductions, which remain claimable. Moreover, for properties built before 1987, the BCI adjustments might be less relevant unless significant renovations have been undertaken. Commercial properties may experience different BCI impacts due to varying construction material costs and standards. Joint ownership and partial-year ownership scenarios can also complicate the application of BCI-related adjustments.

Given these nuances, it's essential to seek professional advice. A Chartered Quantity Surveyor can provide a detailed analysis of how the BCI affects your specific property, ensuring that all potential deductions are accurately claimed. Working alongside your accountant, they can develop a tailored depreciation schedule that maximises your tax benefits and aligns with your investment strategy.

  • Review your current depreciation schedule to identify any potential adjustments due to BCI changes.
  • Consult with a Chartered Quantity Surveyor to assess the impact of the current BCI on your property's capital works deductions.
  • Discuss with your accountant how potential BCI adjustments could influence your tax position.
  • Update your depreciation schedule with any necessary revisions to reflect BCI changes.
  • Monitor the BCI annually to ensure your depreciation claims remain optimised.
  • Consider engaging a professional annually to verify that your deductions are maximised and compliant.
  • Frequently Asked Questions

    What is the Building Cost Index?

    The Building Cost Index (BCI) measures changes in construction costs over time, including materials and labour. It's used to adjust property valuations for depreciation purposes.

    How often does the BCI change?

    The BCI is updated regularly, often quarterly, to reflect current market conditions. Investors should monitor these updates to ensure their depreciation schedules are accurate.

    Does the BCI affect all types of properties?

    Yes, the BCI affects both residential and commercial properties, as it influences the valuation of structural components under Division 43.

    How does the BCI impact my tax return?

    By adjusting your depreciation schedule to reflect BCI changes, you can optimise your capital works deductions, potentially reducing your taxable income and tax liability.

    Are there state-specific variations in the BCI?

    Yes, BCI variations can occur between states due to differing construction costs and market conditions. It's important to consider regional indices when updating your depreciation schedule.

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    Written by Koste Team · Koste Chartered Quantity Surveyors · AIQS Member · RICS Member · TPB Registered · 1300 669 400 · info@koste.ai