Forecast to Complete Calculator

Budget minus spent is a subtraction, not a forecast. This works out the remainder on the rate you have actually been achieving — and shows you the difference between the two answers.

Why the achieved rate

If a package is 60 per cent complete and has consumed 70 per cent of its budget, the honest forecast for the remainder is not the 30 per cent left in the budget. It is the rate you have actually been achieving, applied to the work that remains.

Budget minus spent assumes the rest of the job will behave exactly as planned even though the completed part did not. It takes two seconds to produce and it is almost always wrong.

The three positions

Use this calculator only for packages in progress. A package that is complete needs no forecast — final cost is known, say so and stop. A package not started keeps its budget, unless you already have a quote, in which case use the quote.

The full method is in Forecast to Complete: Why Budget Minus Spent Is Not a Forecast.