The council will slash its figure for planned affordable homes up to 2022 from 4,335 to 1,980 following a new calculation of housing needs.
A planning officer's report said the reduction was due to better data "rather than a reflection of an increase in the supply of affordable housing or a dramatic fall in the number of households in need".
The local development plan's figures were previously based on a local housing market assessment published in 2008. The proposed plan, including the revised figures, is due to be submitted to the Planning Inspectorate for examination in public early next year.
The council has also adopted a new policy aimed at ensuring developers can afford to provide affordable housing through planning obligations.
The policy seeks to reject housing proposals where land has been bought at an "inflated price" that does not consider the extra costs of section 106 planning gain agreements, in which developers commit to fund affordable homes, local facilities and infrastructure.
The report said: "The delivery of affordable housing in financial and viability terms remains challenging in the future unless landowners and developers take full account of the need to provide affordable housing and other obligations at the outset."