The High Pay Centre said some of the country's lowest paid jobs have been the most important during the Covid-19 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 Chichester full-time worker's median salary (£30,000 in 2021) by around 7.30pm on Thursday, January 6 – just the third working day of the year.
This means it would take an average Chichester employee 90 years to earn the annual salary of a top CEO.
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 through the pandemic.
"With the value of the UK economy reduced, there’s also greater pressure to share what we do have more evenly.
"In this context, vast CEO to worker pay differences may be harder to justify."
The average Chichester salary was up from £29,953 in 2020.
Meanwhile, the High Pay Centre said CEO pay had fallen by 17 per cent 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.
Danny Magill, senior research officer at the Equality Trust, said: "In a year where this country has faced unprecedented economic challenges, most CEOs pay packages barely changed, showing how detached high earning CEOs’ have become from the realities of ordinary working people.
"While the taxpayer supported large companies, it was essential workers that kept the economy afloat throughout the pandemic, often for low wages, with no sick pay and at great personal risk."
With women in Chichester earning less on average for working full-time than men (£25,330 compared to £31,683), FTSE 100 bosses will surpass their annual wage in just 31 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 neoliberal think tank, said: "For large companies, a wide array of economic research shows that small differences in top talent have an outsized impact on results. "It’s hardly surprising that they’re willing to offer high salaries to attract the very best in an era of global competition."