HECS isn't charged interest. It only grows with indexation — 2.8% in 2026, the lower of CPI and WPI. That's usually well below what a long-term diversified investment returns. So "pay off debt first" — good advice for a credit card at 20% — doesn't automatically apply to HECS.
The decision is really one comparison: the indexation rate vs your expected after-tax return.
If you do pay extra, do it before 1 June. Indexation is applied that day, so a payment beforehand escapes indexation on the amount paid. A payment on 2 June misses the saving by a year. Note that voluntary payments don't reduce the compulsory repayment assessed in your return — they only reduce the balance and future indexation.
Borrowing capacity. A HECS debt reduces how much a bank will lend you for a home loan, because the compulsory repayment counts against your income. If a mortgage is on the horizon, clearing HECS can help there even when the pure investment maths favours investing — more on that here.
Certainty. Investment returns are uncertain; the indexation saving is guaranteed. Some people rationally choose the sure thing.
→ Compare both paths for your balance — the payoff planner projects your debt-free date and puts "pay extra" against "invest at X%" side by side.