A growing number of people are saving as much as they can to ditch the rat race early and retire in their 30s, 40s and 50s.

The FIRE (Financial Independence, Retire Early) movement is not for everyone. It usually requires that you save and invest up to half of your take-home pay so you can pursue the lifestyle that you want.

These people are not retired in the traditional sense. Many early retirees work part-time on things that inspire them while they earn most of their income from their investment portfolios.

"I like retirement calculators that provide actionable steps to get to where you want to go," said Sam Dogen, creator of the personal finance website Financial Samurai, who retired in 2012 at age 34 after a 13-year career in finance. "Achieving financial independence is really about taking action."

Here are tools developed by early retirees that can help you figure out if that lifestyle is right for you by answering these three key questions:

Why should you retire early?

Many online tools can tell you how much you should save for retirement, but few tell you why. The yFIRECalc can show you the trade-offs between working longer to save more money or retiring sooner to have more freedom.

"I wanted to focus on the time aspect rather the money aspect of early retirement," said Steve, a 57-year-old lawyer who retired at age 48 in Boulder, Colorado, and who updated the yFIRECalc this year after learning JavaScript in his free time. (Since Steve blogs anonymously about the details of his net worth at FrugalFringe.com, he asked that his last name not be used.)

The calculator gives you a snapshot of your life before and after early retirement based on the hours you will spend working, sleeping and left to your own devices.

"It's designed to help make early retirement more tangible," said Steve. "The highest and best use of money is freedom."

Where can you find places to save more?

Peter Adeney, the popular blogger known as Mr. Money Mustache, has built a devoted following of people who strive for early retirement. Nicholas Marrone, a 38-year-old software engineer in Seattle who aims to have enough money to retire at age 47 if he wants, developed six simple calculators to help people live like a "Mustachian" at Mustache Calc.

Many of Marrone's tools focus on the value of reducing your spending because increasing your income only helps when you're working while cutting expenses aids you throughout your retirement.

One big area of savings: eliminating or reducing the cost of owning a car.