Great question! This will ultimately be driven by the income and size of any debt, but I’ve tried to summarise some points below! I hope this helps with your research.

Based on publicly available info from the ATO, a high level summary could be that salary sacrificing on the way in may in a small way reduce taxable income but probably won’t impact any HECS payment; then on the way out, in that year it may increase your HECS payment if you’re paying 30%+ tax.

Given the size of the FHSS is capped at $15k per year, it may be fair to say the dollar impact to your cash flow will be nominal; then the increased HECS payment in the year you withdraw (say you withdraw a max+interest amount of circa $65k in 8 years time), will mean that your HECS payment in that year may be higher than normal.

If you’re trying to compare post tax contributions vs salary sacrifice, aside from the timing differences again may not really make much difference.

There is nothing to show it will impact your eligibility.

Some reading

https://www.ato.gov.au/tax-rates-and-codes/st...

https://www.ato.gov.au/individuals-and-famili...

Thanks!