Taxes are calculated as follows:-
Level 1: 0% under 8,000,000
Level 2: 10% over 8,000,000 to 20,000,000
Level 3: 20% over 20,000,000 to 50,000,000
Level 4: 30% over 50,000,000 to 80,000,000
Level 5: 40% over 80,000,000 and over
However if you are working less than 183 days in vietnam you pay a flat rate of (I think) 25% on everything you earnt in vietnam.
If you are resident in Vietnam for tax purposes (you have to be somewhere and if you aren't in Aus then you most likely will be considered to be here) then you have to pay tax in vietnam on your worldwide earnings. How they would know you had earnings elsewhere I dont know, but not declaring it is tax evasion.
Hope that helps
Just closed my Vietcombank account and I would strongly recommend not to have too much money in country. Saw a lot of foreigners today who could not get their own money back in their own currency, only in VND and saw an equally big crowd of vietnamese people methodically asking for the balance of their account and then withdrawing their money. So just have a look at some of the posts on this website about the availability of USD, the inflation etc. and you will see what I mean.
As far as tax goes, if you are in the business sector you will have to pay tax (over income earned in VN), but working in the NGO sector or for UN, Worldbank, EU etc. this is still not sorted out clearly.
WARNING !
A new decree related to PIT (Personal Income Tax) has been issued on 8 sept 2008.
Will be applicable for January 2009.
Every vietnameses and foreigners will be taxable on the same basis since the first VND earned including every allowances paid by their employer. A financial bomb !
New taxes are as following on a monthly basis in million VND :
1 Up to 5 5%
2 Over 5 to 10 10%
3 Over 10 to 18 15%
4 Over 18 to 32 20%
5 Over 32 to 52 25%
6 Over 52 to 80 30%
7 Over 80 35%
It's a progressive rate calculation : PIT is calculated by applying rates for each bracket.
Check out on google with the decree number as keyword : 100/2008/ND-CP
Sorry the bad news !
Duc de Hanoi