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Business use share calculator

Apportion an eligible cost by its business use share. It does not decide deductibility, depreciation or records.

Published 20 September 2026. Last reviewed 27 September 2026.

Business use share inputs
Enter the inputs and calculate.

Sources applied

  • Formula: business use share = eligible cost × business use percentage / 100, rounded to cents.
  • Figures: supplied by you. No statutory rate or threshold is applied. The cents per kilometre rate is a separate table and is not applied by this calculator.
  • Not determined here: deductibility, depreciation and whether the records support the percentage.

How it works

Eligible cost × supported business use percentage / 100. This apportions the amount you supply. It does not determine deductibility, depreciation or record sufficiency.

For car expenses under the cents per kilometre method, the rate by income year is kept as a maintained table on this site.

Phone and internet record checklist

One of the nine business calculators. Calculations run in this browser. The calculator code does not send your inputs to a server or save them automatically. To check, disconnect from the internet once the page has loaded, then calculate.

Planning estimates in AUD. Confirm tax treatment, liability amounts and dates separately. Amounts round to the nearest cent, with exact half cents rounded up.

Written by Ryan Duguid in his own time and on his own equipment. He is a Provisional CA ANZ Member. CA ANZ has not endorsed this site or its tools.

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Ryan Duguid is not a registered tax agent or BAS agent. Nothing here is tax, legal or financial advice. Computational outputs are review aids for a qualified professional, not compliance determinations, and lodgement decisions stay with a human.

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Ryan Duguid, ABN 59 834 031 764

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