You have reached Coast FI when your invested balance, with no new contributions, is on track to grow to your retirement target by your chosen year. The check is one line: target ÷ (1 + real return) raised to the number of years left.
Retirement saving has two useful paces: a long steady hill and short hard intervals. Coast means your nest egg can grow mostly on its own while contributions ease up. Sprint means you push hard now to buy that easier hill later. This is for people stuck between grinding forever and quitting contributions too early.
You will see how to tell which pace you are on, and how to test a coast year versus a sprint year on the same timeline before you change payroll deductions.
Coast, in plain terms, is when invested balances are already large enough that growth alone can reach your retirement target if you stop or sharply cut new contributions. Sprint is the opposite stretch: balances are still light, so the years in front of you need high savings rates to catch the goal. Same destination. Different slope.
Example: you are 34 with $180,000 invested and a rough target of $1.2M by 60, so 26 years out. At a 7% real return, the coast number is about $207,000 ($1.2M ÷ 1.07^26), so $180,000 is close but not there. At 5%, it is about $337,000. The return assumption matters more than the formula. Someone with $40,000 at the same age is still in interval territory. Copying a coast blog post while you are mid-sprint is how contributions stall too soon.
Coast is not “never save again.” It is permission to ease the interval intensity: fund a house, cut hours, or pause the side hustle while the long hill does more of the work. Sprint is not punishment. It is a timed push with an end condition, like hitting a match max or a portfolio milestone.
Use a real (after-inflation) return, not a nominal one. A 7% nominal return with 3% inflation is closer to 4% real, which pushes the coast number way up. And coast still means earning enough to cover today's bills and health insurance until you actually retire.
Write the target spend and the target year before you pick a pace. Without those, coast and sprint are just moods.
Illustrative balance at age 55
If you want to sprint, define the interval. Twelve months at 25% savings. Or maxing a 401(k) and IRA until the balance hits $250,000. Put the higher transfers on a projection and check that checking still survives bill weeks. A sprint that creates credit card debt is not a sprint. It is a leak.
If you want to coast, define what eases. Drop from 18% to 8% contributions while the portfolio compounds. Model whether the retirement year still holds if returns are average, not magical. Keep enough saving to capture an employer match. Leaving free match dollars on the table is a steep price for a softer hill.
Many people alternate. Sprint while costs are low, or while two incomes and no kids make it easy. Coast contributions during a parental leave year. Sprint again when daycare ends. The timeline should show those gears shifting on purpose, not by accident after a chaotic year.
Revisit after a raise, a home buy, or a market year that changes the balance a lot. A sprint that already hit its milestone can become a hill. A coast plan that assumed low housing costs may need another interval after a mortgage.
Flan projects retirement and brokerage balances alongside income and expenses. You can lower contributions in one scenario and raise them in another, then see whether the long hill still reaches the year you care about.
Coast is a long steady hill. Sprint is a set of hard intervals. Name your target year, test both paces on a timeline, and shift gears when life does.
The right slope is the one that still works next month and decades out. That is the whole comparison. To turn the target into a date, read Early retirement is a date. The FAQ covers how Flan handles real vs nominal returns.
Try the free money calculators from Flan.
Flan is planning software, not a bank, broker, or licensed advisor. Nothing here is financial, tax, or legal advice.
Read more Flan Files at theflan.app/blog.
