Most retirement calculators assume you work and save every year until you retire. This one lets you add the gaps: a sabbatical, a year of travel, parental leave, or a few months to start a business. For each break you set when it starts, how long it lasts, and what you spend per month while you are not earning.
The calculator then projects your net worth with and without the breaks and shows the difference at your retirement age. Turn on retirement spending in the advanced settings to see your earliest financial independence age, based on the 4% rule.
A break costs more than the money you spend during it. You also lose the contributions you would have made and every year of compound growth on both. That is why the same break costs more when you are younger.
Projections are estimates, not financial advice. Returns are assumed constant; real markets are not.