The songwriter has just posted a set of results for the two companies that handle her income.
They reveal she has amassed a multi-million-pound fortune just a few years after playing gigs in Glasgow coffee shops.
Latest accounts show her main company, Amy Macdonald Ltd, has £2.9m in the bank. Her second company, Amy Macdonald Touring Ltd, has £2.04m in another account.
The combined funds of the firms for the period up to April 2013 are more than £1m up on the previous year's figures.
The accounts, filed at Companies House, show Macdonald has an investment portfolio worth £950,000. She also takes out a yearly loan from her main company of about £200,000.
The 26-year-old, from Bishopbriggs near Glasgow, released her third album Life In A Beautiful Light, last year.
Her records have sold millions of copies and she has become a massive star in European countries such as Germany and Denmark as well as the UK.
A financial source said: "These figures show that Amy has had yet another successful year and increased the value of her companies by more than £1m.
"She will also have personal earnings which are not channelled through the companies, making her even richer.
"She writes all of her own songs, which entitles her to a large slice of the royalties from her records."
Macdonald set up the firms more than six years ago, soon after signing her first record deal.
She revealed she had bought a £170,000 Ferrari 458 to add to her car collection. She also owns a Range Rover and a Bentley.
In 2011, she purchased a £800,000 luxury home in Milngavie, East Dunbartonshire. The singer was unavailable for comment.