When planning the Union Budget for 2017-18, the finance ministry will have its work cut out. It has many imponderables to confront. The impact of demonetisation is not captured by the Advance Estimates of national income, a fact that complicates the process of budgeting. The roll-out of the goods and services tax is planned for the coming financial year, which means that revenue during the year will exhibit an analytical discontinuity with what has gone before. And the removal of the distinction between Plan and non-Plan expenditure, while much needed, will confuse analysis of what spending counts as an investment