Courts expect a third of offenders won't pay a new $50 levy to be imposed on all offenders next year.
The fee, which comes into affect from July next year, will apply equally to anyone convicted in a court.
Collections general manager Bryre Patchell told the Justice and Electoral Committee on Thursday that the Ministry of Justice expects to collect $13.6 million over four years from the levy.
There are 120,000 sentencings in the courts each year. If every offender paid the levy, that would generate about $6 million per year.
Mr Patchell says they estimate 68% of offenders will pay. He says it will cost about $2 million to set up the scheme and $1 million per year to run it.