How budget projections change

Finance Minister Bill English, with Prime Minister John Key, on his way to the House to read the 2015 Budget. Photo / Mark Mitchell

Each year government lays out projections for the next five years. Keith Ng's special data blog post for the Herald looks at how these differ each year.

Every budget looks at historical trends and forecasts the future, but what about the history of the forecasts?

These tell us when "the future" changed, and provide strong clues as to why it changed.

For example, we know that the Christchurch earthquake was a huge cost for the government, but how did it change our long-term debt track?

Bill English says unemployment is going to drop below 5% soon, does that mean we're doing well? Better than last year? What has actually changed?

This visualisation was created by combining every Treasury Fiscal Strategy Model since 2008 into a single series, and contains all the data from today's Budget.

Note that some data series could not be used because the data was not comparable across the time-span.