How these guides are researched

Every figure on this site comes from named, dated legislation or the government agency that administers it. Where no published figure exists, we say so rather than estimating.

Where do the figures come from?

What counts as a source?

What happens when there is no published figure?

How often is a guide rechecked?

What does the model itself assume?

What is not modelled?

How do you handle a rule that is unclear?