Working out Weekly Shortfall – (Correct Method for Budgeting Property Cashflows inclusive of tax deductions)

I'm keen to ensure I am using the correct method to working out cashflows.
When involved with negatively geared property, it is important to know how much of one's "Own Money" is required to be added to keep the investment afloat.

Ive seen and used fancy spreadsheets and Property Investment Analysis (PIA) software but Im not confident in their accuracy and would rather know the correct formula myself.

I also don't like using say "average rate of 30c" ….

The method I have used is as follows (with an example provided):

-Property renting for $290/w
-Taxable Income outside of Property of $57,500 (ie salary as employee minus non property deductions)
does not include the rent.
-tax payable on this $57,500 income would be $11,712  (taken from taxcalc.com.au)

PROPERTY DETAILS:
(yearly figures listed)
(only "main" expenses listed  – I appreciate their are others. lets k.i.s.s.)
(ownership is in sole name 100%)

Rent $15,080

Interest $11,722
Council Rates: $2000
Property Agent Fee $1244
Depreciation: $3,000
Total Deduction: $17,996

The Loss: $17,996 – $15,080   which is total deductions minus the rent
Loss: $2,886

Now, the loss gets minused off the original taxable income of $57,500 – thus making the taxable income $54,614.  According to taxcalc.com.au the tax payable on that taxable income of $54,614 is $10,687.

Therefore the negative gearing tax refund would be the difference between the tax payable on the (original) taxable income of $57,500 vs the taxable income of $54,614?
So that's $11,712 – $10,687 = $1025

So , I add the tax refund to the loss
$2,886 – $1,025 = $1861

Therefore, the property is negatively geared to the tune of $1,861 or $35 per week.

Can I have confirmation that my method above is correct?
Cheers
Noddynol