Tax breaks for companies undertaking research and development and superannuation payments for veterans and public servants have overshot expectations, adding billions of dollars in spending to the federal budget.

The R&D Tax Incentive returns money to businesses that invest in developing new products and services. Rebates are expected to increase by nearly $500 million next year and $2.6 billion over five years from 2023-24 to 2027-28, the budget papers show.