The average National Disability Insurance Scheme participant uses about 58 per cent of their entitlements, according to figures compiled by economic research organisation the e61 Institute.
Meanwhile, more than a third of users (34 per cent) leave more than half their allocated budgets untouched.
"Some degree of underspending is expected because plans need buffers so participants can get all the care they need," e61 Institute research manager Pelin Akyol said.
"But such a large degree of underspending among a third of participants may suggest that participants are struggling to access services or plans are not always aligning with people's needs."
The findings paint a different picture from National Disability Insurance Agency figures showing 74 per cent of budgeted funds across the scheme are spent.
That headline rate, published by the agency in June, obscured large differences between individual users, researchers said.
Much of the 74 per cent figure is driven by people in supported independent living, who make up about five per cent of participants but account for a disproportionate share of spending and utilisation.
The study analysed data from plan manager Kismet, covering almost 6000 finished plans between January 2025 and September 2025.
It suggests access to services cannot be blamed for under-utilisation, with geography playing only a minor role in individual differences.
Participants in outer regional areas spent about six per cent less of their budget than those in major cities, but most of the variation occurred within areas rather than between them.
Awareness and familiarity likely play more significant roles, as spending rises the longer a user participates in the scheme.
"We see a clear learning curve as participants use more of their plan the longer they are in the scheme," Dr Akyol said.
How funding is structured also shapes outcomes, with participants who can shift money between supports often better matching it to their needs.
In more tightly restricted categories, funds are more likely to sit unused.
"This suggests that initial allocations may not perfectly reflect real-world support needs," e61 Institute research economist Theo Gibbons said.
"If plans are too rigid, they can leave participants with unused funds even when they still have unmet needs."
The NDIS provides funding to more than 500,000 Australians with permanent and significant disabilities.
It is one of the fastest-growing areas of federal spending, costing more than $40 billion a year.
