Every winter, Alan and Katie Donegan would avoid turning on the heating at their home in the south of England.

"Instead, we wore extra layers and used hot water bottles - we turned it into a game," says Alan. "It wasn't suffering, it was strategy."

While the couple admit that others thought they were "extreme" or "mad" to put so much emphasis on not spending money, Alan explains that they were "laser-focused on buying freedom".

By "freedom" he means early retirement, which the Donegans managed to achieve seven years ago when Alan was only 40, and Katie just 35.

The two rarely had takeaways and always took packed lunches to work. "We were £40,000 better off over 10 years from just that one lunch habit," says Alan.

"We even charged our phones while out and hunted for discarded Nectar [supermarket] vouchers. You can decide if that's crazy or genius, but it worked."

Alan had worked as a landscape gardener before launching a training and life-coaching business, while Katie was an actuary, or risk assessor, for a financial firm.

Aside from their good incomes, their extreme saving habits meant they were able to retire early - and they put as much money as they could possibly afford into investments.

"Every pound we invested was a step closer to the life we wanted," says Katie. They quit work after their savings hit £1m.

Alan and Katie are part of a small but growing global movement called Fire, which stands for "Financially Independent, Retire Early".

What was a little-known concept 15 years ago is now home to almost a million members on the main Fire discussion board on the social media site Reddit, and mainstream financial institutions publish numerous guides on the topic.

The central tenet is to live extremely frugally during your working life so you can retire as soon as possible.

For most of us, being able to leave the working world early is just a dream. From the current high cost of living to elevated property prices and student debt, we will be working longer, not less. The statistics back this up.

Last year, average retirement ages in the UK hit record highs of 65.8 years for men and 64.7 for women, official data showed.

It is a similar situation in the US, where the average retirement age for men and women has increased steadily since the 1990s, to 64.8 and 63.3, respectively, in 2025, according to one long-term study.

Yet devotees of Fire, such as 49-year-old Amy Minkley, are committed to their goal. The American middle-school teacher was able to retire at just 44.

To help achieve this, she worked abroad at international private schools in Japan, Singapore, India and Thailand, where Minkley says she was able to earn more money and enjoy much lower living expenses than back home in Texas.

She also spent as little as possible. "I wasn't interested in keeping up with a certain expat lifestyle," says Minkley.

"I rarely bought expensive clothing, kept electronics until they gave out, cooked most of my meals at home, and paused before any significant purchase.

"Having a housemate while living in Singapore and India allowed me to save even more, and in several countries I didn't need a car, which kept my expenses low," she says.

Minkley now lives in Bali, where her retirement income goes further than it would in the US.

Carol Schleif is chief market strategist at BMO Private Wealth, a Toronto-based financial advisory business.

She says that while Fire is "still doable" for many people, most of her clients are focused more on having balance in their working lives. So instead of rushing to retire as early as possible, they are focusing on combining a meaningful career with living within their means.

"If you retire early but don't have friendships, health or a sense of purpose, you've achieved one goal but sacrificed other things… you have to wonder if it's worth it," says Schleif.

"People are [instead] having a more flexible approach these days. They are trying to find ways to reach their retirement goals but also enjoy life."

Sarah Coles, head of personal finance at UK investment platform AJ Bell, warns that making the Fire philosophy work is increasingly challenging as most people simply cannot afford it.

Still, she says that several Fire principles are worthwhile, and can help people retire a little sooner, such as starting to save money as a young adult, and increasing your pension payments after every pay rise.

"A balanced path can get you the retirement you want, when you want it, without breaking your spirit. It just needs to be more nuanced and realistic," says Coles.

Within the Fire community, some are now following this less intense route, leading to the creation of sub-genres such as "Barista Fire". This focuses on saving enough money so that your investment income can cover most of your living expenses. You then top this up with part-time work.

For some Fire followers, though, extreme frugality is still the main way to achieve early retirement, and a sacrifice they see as worth it in the long term.

As Minkley puts it: "The principles of Fire are simple, and they haven't changed - spend less than you earn, invest the difference, and give your money time to grow."