Search for the best Coast FIRE calculator and you’ll find a dozen options that all run the same core formula — so what actually separates them is the experience: how fast you get an answer, whether you can see the crossover point on a chart, and whether the tool handles real-world wrinkles like Social Security or a spouse. We compared the five most useful free options in 2026, including our own, with an honest look at where each one shines.
Full disclosure up front: this site is option #1. We built it because we wanted specific things the others didn’t offer — but each tool below is genuinely good at something, and the right choice depends on your situation.
Quick Comparison Table
| Calculator | Real-time results | Interactive chart | Social Security / pension inputs | Couples mode | Sign-up required |
|---|---|---|---|---|---|
| CoastFireCalculator.org | ✅ Instant | ✅ Hover tooltips + coast marker | ❌ (guides instead) | Combine manually | No |
| WalletBurst | ✅ Instant | ✅ Sliders + crossover chart | ❌ | Combine manually | No |
| Clark.com | ✅ Instant | ✅ Year-by-year projection | ✅ Both | ✅ Built in | No |
| Marriage Kids and Money | ❌ Calculate button | ✅ Contributions breakdown | ❌ | Combine manually | No |
| The Fioneers | Spreadsheet | ❌ | ❌ | Combine manually | Email for download |
1. CoastFireCalculator.org — Best for Instant, Visual Answers
We’re obviously biased, so we’ll let the features speak. Our Coast FIRE calculator was built around one idea: you should see your answer change as you type, with no calculate button and no page reloads.
What it does well:
- Real-time results — every keystroke updates your Coast FIRE number, your coast status, and the projection chart instantly
- Interactive chart with hover tooltips showing your projected balance at any age, plus a visible marker at the exact point your investments cross the coast line
- Coast-by-age pages — precomputed numbers for every age from 20 to 65, useful for quick benchmarks without touching a calculator
- Works in today’s dollars — converts nominal returns to real returns (1 + nominal) ÷ (1 + inflation) − 1 automatically, so your spending target stays in current purchasing power
- Free, no sign-up, no email gate, and mobile-friendly
Where it falls short: it doesn’t model Social Security or pensions inside the tool itself — we cover those adjustments in written guides instead (Social Security, pensions). It’s also a single-scenario tool; there’s no Monte Carlo simulation.
2. WalletBurst Coast FIRE Calculator — Best Established Tool
WalletBurst’s Coast FIRE calculator is one of the originals, and it’s still excellent. It’s slider-driven: drag the investment return, inflation, and safe withdrawal rate sliders and watch the chart react immediately.
What it does well:
- Instant feedback via sliders — great for building intuition about how sensitive your number is to each assumption
- Clear dual-line chart: a green line for your projected net worth and a blue line for the Coast FIRE target at each age; when green crosses blue, you’re coasting
- Inflation built in — it subtracts inflation from your growth rate so everything stays in today’s dollars
- A whole ecosystem of companion tools (FIRE calculator, Barista FIRE calculator, net worth tracker)
Where it falls short: the slider-based inputs make entering precise figures a little fiddly compared to typing, and like ours, it doesn’t model Social Security or pension income directly. Still, it’s a rock-solid, credible tool — if you use two calculators to double-check your number, this is a natural second.
3. Clark.com Coast FIRE Calculator — Best for Social Security, Pensions & Couples
The calculator at Clark.com (from Clark Howard’s personal finance site) is the most feature-rich of the bunch, and the one we’d point you to if your situation has moving parts beyond a simple portfolio.
What it does well:
- Social Security inputs — expected monthly benefit and claiming age are built right into the projection
- Pension support — model guaranteed income alongside your portfolio
- Couples mode — model a single person or a couple combining savings and benefits
- Advanced knobs: life expectancy, separate post-retirement return rate, annual savings increases, and results in both today’s and future dollars
- A year-by-year breakdown of how your money grows
Where it falls short: more inputs means more decisions before you get an answer — if you just want a quick “am I coasting yet?” check, the extra fields can feel like homework. The interface is also more form-like and less chart-forward than WalletBurst or ours. But if you want Social Security in the math without doing the two-bucket adjustment by hand, nothing else on this list comes close.
4. Marriage, Kids and Money Coast FIRE Calculator — Best Guided Experience
Andy Hill’s Marriage, Kids and Money site offers a Coast FIRE calculator with a distinctly family-friendly flavor — fitting, since Andy famously paid off his mortgage and hit Coast FIRE while raising two kids.
What it does well:
- Guided, step-by-step inputs — about ten short, plain-English questions walk you through every assumption, which is great if you’ve never used a FIRE calculator before
- Instant red/green verdict — results show immediately whether you’re below or above your coast target, plus your projected retirement balance and the annual income it supports
- Chart with contribution breakdown — the graph separates continued contributions from post-coast growth, a nice visual touch most tools skip
Where it falls short: results require clicking a calculate button rather than updating live, and there are no Social Security or pension inputs. For a first-timer who wants to be walked through the process, though, it’s the gentlest on-ramp on this list.
5. The Fioneers Coast FI Calculator — Best for Spreadsheet Lovers
Jess and Corey at The Fioneers helped popularize the term “Coast FI,” and their calculator is different from everything else here: it’s a downloadable spreadsheet, offered free in exchange for your email address.
What it does well:
- You own it — a spreadsheet lives on your machine, works offline, and can be customized endlessly: add scenarios, track your number over time, extend the formulas
- Conservative by design — it defaults to a cautious ~5% real growth assumption, which builds in margin automatically
- Paired with excellent education — their Coast FI content explains not just the math but how to use the milestone to design a life you don’t want to retire from
Where it falls short: no interactive chart, no instant web-based answer, and the email gate means it’s not truly frictionless. If you love building your own models, our Coast FIRE formula guide includes a one-cell spreadsheet formula that replicates the core calculation.
How We Evaluated
To keep this comparison fair, we ran the identical scenario through every tool: age 35, $150,000 invested, $500/month contributions, $45,000/year retirement spending, retiring at 65, 7% nominal return, 3% inflation, 4% withdrawal rate. (The expected Coast FIRE number at 35 under those assumptions is $1,125,000 ÷ 1.0388^30 ≈ $358,720 — you can verify that with the formula in our Coast FIRE formula guide.) Tools that landed near that figure passed the smell test; we then judged them on speed to answer, chart quality, input flexibility, and whether results stay in today’s dollars.
One category we deliberately excluded: full-blown retirement planners like Boldin or ProjectionLab. Those are excellent (and often paid) planning suites, but they’re overkill when you specifically want a Coast FIRE number, and they deserve a separate comparison.
How to Choose
Pick based on the question you’re actually asking:
- “What’s my number, right now, with a visual?” → CoastFireCalculator.org or WalletBurst
- “How do Social Security, my pension, or my spouse change the picture?” → Clark.com
- “I’ve never done this and want to be walked through it” → Marriage, Kids and Money
- “I want a model I can keep and customize for years” → The Fioneers spreadsheet
One more tip regardless of which you choose: run your numbers through two calculators. The formula is deterministic, so if both tools get the same inputs, they should agree almost exactly. If they don’t, one of them is treating inflation or returns differently than you assumed — and that’s worth knowing before you make career decisions based on the output. Whichever tool you land on, revisit your number once or twice a year: markets move, spending changes, and your Coast FIRE number is a living target rather than a one-time answer.
The Bottom Line
There is no single “best” Coast FIRE calculator — there’s the best one for your question. For most people most of the time, a fast, visual, today’s-dollars answer is what matters, which is exactly why we built ours the way we did. Try the Coast FIRE calculator now, cross-check with WalletBurst or Clark.com, and then dig into the strategy guides on our blog — including Coast FIRE for couples and Coast FIRE vs Barista FIRE — to turn the number into a plan.