The Tax Policy Changes document, published as part of Budget 2025, sets out the first and full year cost of Budget 2025 tax policy measures. The carryover cost is calculated from the difference between the first year cost of the measure (2025) and the impact on a full year.
The impact of carryover is reviewed as part of the budgetary process, with a number of factors to be considered, including the take-up of the measure which could impact the expected cost of the measure. This is reflected in the budgetary parameters set out in the Summer Economic Statement.
Furthermore, the cost of tax expenditures are reviewed annually in the Tax Expenditures report, which was published in July 2025.