Both renters and landlords have left more than $37 million of unclaimed tenancy bonds sitting in the Government's coffers, with people either not bothering to claim the money back or simply forgetting about it.

Figures obtained by RNZ News show that as of November there was $37.3 million in unclaimed bonds, and a further $16.2 million in uncollected bonds, which have been authorised to be refunded but are sent to the wrong address or bank account.

Overall unclaimed bonds have increased six-fold since 2012.

The Tenants Protection Association's Helen Gaytoni believed the increase was being driven by rising rents and landlords asking for bigger bonds.

"A lot of land lords didn't charge the maximum four weeks rent for a bond, they used to charge only one or two weeks but now it is very uncommon for a landlord not to charge the four weeks which they are able to."

Ms Gaytoni said the process to collect bonds was easy, but people were still failing to do so.

"Generally people can't be bothered, they have the attitude that it is to hard or there has been a claim against the bond which they have not followed up or has not been contested and they don't think it is worth it so they've just left it," Ms Gaytoni said.

Any money that was left unclaimed for more than six years was deemed public money and held on behalf of the Crown

Ms Gaytoni said the money could be used to prevent unclaimed bonds increasing.

"That money needs to be put into advocacy, such as organisations like ours or into education of tenants so these things stop happening."

Tenants are not the only ones missing out. The Property Investors' Federation said some landlords were owed money, but just could not be bothered.

Chief executive Andrew King agreed the money should go towards improving tenancy services.

"It would be good if the government used the money to enhance the tenancy tribunal system or to help pay for the tenant and landlord associations, both groups are not for profit, do a lot of good work but they are underfunded."

No one from The Ministry of Business, Innovation and Employment was available for an interview with RNZ, but in a statement it said it was exploring better ways to help both tenants and landlords who think they are owed money.