Scotland needs almost 500,000 migrants in the next 20 years to achieve the same balance of pensioners and working-age adults as the UK, according to the Treasury.
The ageing population and the implications on migration is one of five key areas considered in the Treasury's latest analysis assessing an independent Scotland's fiscal position between 2016 – the first year of independence – and 2035/36.
Scotland's population is projected to age more rapidly in the future compared with the UK as a whole.
The Treasury considered net annual migration which would be required in an independent Scotland for it to achieve a "dependency ratio" equivalent to that projected for the UK for two decades.
The dependency ratio is the number of people predominantly receiving from the State – pensioners – versus the people paying taxes into the State – working-age adults.
The Treasury says post-independent Scotland needs to treble its net annual migration from 7,000 to 24,000 to match UK demographics.