The High Pay Centre said some of the country's lowest-paid jobs have been the most important during the pandemic, and that income inequality may now be harder to justify.
The think tank estimates the median annual pay of FTSE 100 CEOs was £2.7 million (around £827.69 per hour of their 12.5-hour days) in 2020 – the latest data available.
Assuming they start work at 8.30am, they had already earned a Northumberland full-time worker's median salary (£28,229 in 2021) by around 5.30pm on Thursday, January 6 – just the third working day of the year.
This means it would take an average Northumberland employee 95 years to earn the annual salary of a top CEO.
The 13 best beaches in Northumberland as ranked by Tripadvisor
Fun in the sun at Blyth beach
The 14 best beaches in Northumberland as ranked by TripAdvisor reviewers - and 6 stunners which didn't make it
29 of the best places for Sunday lunch in Northumberland
Amble basks in the sunshine as heatwave hits
The median is used to stop figures being skewed by particularly small or large wages, and it is assumed that CEOs work 62.5 hours a week.
High Pay Centre director Luke Hildyard said: "Covid-19 has shown how much we all depend on each other. Some of the lowest-paying jobs have played the most important role to keep society functioning.
"With the value of the UK economy reduced, there’s also greater pressure to share what we do have more evenly.”
The average Northumberland salary was down from £28,472 in 2020.
Meanwhile, the High Pay Centre said CEO pay had also fallen by 17% from £3.3 million in 2019, making it the first time since it was founded in 2011 that CEOs have needed to work into a fourth day to earn the same annual pay as a full-time worker in the UK.
With women in Northumberland earning less on average for working full-time than men (£26,897 compared to £29,492), FTSE 100 bosses will surpass their annual wage in just 32 hours.
The Adam Smith Institute said the shrinking gap between top and median pay was driven by "public relations concerns", difficult economic circumstances in the pandemic, and pressure on firms that received furlough support.
Daniel Pryor, head of research at the think tank, said: "A wide array of economic research shows that small differences in top talent have an outsized impact on results.
"It’s hardly surprising they’re willing to offer high salaries to attract the very best."