Confused about Tax.

[The[cookie]Doctor]

Not sure if anyone can help me.
I have been playing around with the look of our finances etc just to make sure everything looks ok and well, I am totally confused about Tax.

So, basically I have three sources of income.
I took the Jul-Sep quarter total for these incomes, and multiplied by 4 to get myself an adjusted estimate of income.
Also I have multipled the tax withheld as this should total tax withholdings at the EOFY, right?

But then... I am looking at how much tax one should pay. It says $4650 up to $37000 and 30c per dollar thereafter.
And so I used that to work out that - for example, and income of $70k should pay $9900 + that $4650 previously mentioned.
= tax to bed paid $14550.

But my multiplied numbers equal some thousands less than they should. So I don't get it???
I checked the tax tables per each source to make sure I am getting taxed correctly so I am not really sure how it works out to be wrong =/

Can someone enlighten me I know I am overanalysing and I can get my employers to withhold more and then offsets might work out anyway but I'm stressing about having a debt.

[Astrid]

Ok, it is not straight forward.

Each pay you are paid as per the tax tables and what you have selected to be taxed at (tax free threshhold, HECS/HELP etc)
The tax withheld will be up and down if you income is up and down and sometimes by the end of the of the amount will be under or over what you should have been taxed. I have seen this happen a lot with those with HELP debts.

The tax tables do not just include the standard tax rates, they also include the flood levy(which will increase the tax you pay) and other components, such as the low income tax rebate (which will lower the tax you pay)

The best thing to do to work out what you should be taxed over the year is to work out your yearly income estimate (as you have done). Then divide it by 12 (for monthly amount). Go onto the ATO tax calculator, select all your options (tax free threshold, HELP etc). Get the tax amount and then times it by 12 to get your estimated tax for the year.

So for example of $70,000
$70,000 per month = $5833.33
Tax per month = $1,313 (just claiming tax free threshhold)
So tax for the year = $15,756

If you think you may not be paying enough tax due to multiple jobs etc, then you can ask an employee to withold more tax for you, most accounting/payroll system can do this automatically and it is less than 5 minutes for them to set-up the amount against your file. There is a Upward Variation form on the ATO site that you can complete to get this done.