Going to the source suggests it&#x27;s the estimated cost of the entire rollout from 2010-2021<p>That&#x27;s an entire rollout which entails designing, building and operating a payments system in parallel with several different existing systems it replaces, all the extra non-dev staff needed to keep things running and identify who gets which payment entitlements when, and all the additional administrative costs, which presumably involves an awful lot of explaining to the public how their benefit entitlements have changed. Actual software development probably accounts for a relatively small proportion of that. The status quo admin costs £3.5bn per annum, so an extra billion a year actually isn&#x27;t as big a deal as it sounds.<p>If we can simplify all that down to a &quot;bloated Java app&quot; then we can certainly dismiss Facebook as a PHP web forum and suggest that its running costs don&#x27;t compare particularly favourably, even if it does serve an awful lot of ads.<p>Judging by the reports of delays and admin cockups, if anything the UK government has probably underspent.