Notional Deductions are 'theoretical deductions'.  According to the Australian Taxation Office (ATO), a Notional Deduction can not be deducted like a general deduction, for example using Section 8-1 of the Income Tax Assessment Act 1997 (ITAA 1997).

In terms of the R & D Tax Incentive, a Notional Deduction is used to calculate the amount of a Tax Offset that an entity may be entitled to, rather than an actual deduction amount.