The school, which has around 1,700 pupils on its roll from nursery age through to secondary school, saw its income rise by some £3.65m on the year before.
Its accounts show that in 2015 it benefited from £3.2m in donations and legacies.
A spokeswoman said that donations from more than 100 philanthropists had helped achieve the figure for the school where fees are up £12,000 a year.
Oil tycoon Sir Ian Wood led the way with a £2.5m gift towards the creation of The Wood Foundation Centre for Science and Technology, the largest teaching centre of its kind in the UK.
The spokeswoman added: “During this period over 100 philanthropists supported a campus development project donating funds to enable the creation of The Wood Foundation Centre for Science and Technology alongside The Craig Centre for Performing Arts.”
Many of Scotland’s fee-paying schools are charities. Analysis of figures from the Office Scotland Charity Regulator (OSCR) shows that Fettes in Edinburgh was the second single highest earning private school in Scotland last year.
It spent £1.9m on raising funds and £15.6m on charitable activity, namely education. Fettes benefitted from around £426,000 in donations and legacies over the period.
Meanwhile, Gordonstoun near Elgin in Moray recorded income of £16.47m in 2015. It was the third-highest single amount raised by a private school last year.
The school, whose past pupils include Prince Charles and the Duke of Edinburgh, received donations of around £280,000.
Its fees for older boarders are currently £10,700 a term with the school having approximately 600 pupils.
George Heriot’s in Edinburgh had the fourth single highest income last year at £15.4m. The day school, which has around 1,700 pupils, has fees of up to £3,565 a term.
Other high-earning Edinburgh schools are those run by the Merchant Board of Education - Mary Erskine, Stewart’s Melville College and George Watson’s College.
Their combined income in 2015 was £57.1m but no figures for the individual schools are available.
Other private schools with the highest recorded incomes in 2015 were Glasgow Academy (£14.8m), Hutchesons’ Grammar in Glasgow (£14.6m), Dollar Academy (£13.3m), Strathallan (£13.1m) and Loretto in Mussleburgh (£11.9m).
St Leonards in St Andrews has not yet lodged its income for 2015 but the 2014 figure was £14.95m - up more than £6m on the year before.
Independent schools have had charitable status since 2005, a position which gives them business rate relief, unlike state schools, and an exemption from corporation tax on charitable earnings.The Scottish Council for Voluntary Organisations has called for a review of the current system which “allows some charities to restrict access to services through high fees which exclude the majority from benefitting.”
In 2014, OSCR found that all 52 independent schools then on its books passed the “charity test” . Originally 10 had failed due to fees which restricted access to young people from less-well off backgrounds.
The 10 independent schools with the highest single recorded incomes 2015 *
1. Robert Gordon’s College, Aberdeen. £20.6m
2. Fettes College, Edinburgh. £18.9m
3. Gordonstoun, Elgin. £16.5m
4. George Heriot’s, Edinburgh. £15.4m
5. Glasgow Academy (£14.8m)
6 Hutcheson’s Grammar, Glasgow (£14.6m)
7. Dollar Academy (£13.3m)
8. Strathallan (£13.1m)
9 Merchiston Castle, Edinburgh (11.2m)
10. Glasgow High (£10.8m)
*list does not include 2015 figures for three schools run by the Merchant Board of Education - Mary Erskine, Stewart’s Melville College and George Watson’s College. No individual breakdown on individual school income is available but together they raised £57.1m in 2015.