Coast FIRE calculator

How this calculator works

This calculator estimates the Coast FIRE threshold—the invested balance needed today that could grow to your retirement target without any additional contributions. It starts with your retirement spending goal and withdrawal rate to calculate a future portfolio target, then discounts that target back to today's dollars using your current age, planned retirement age, and assumed real return.

Coast FIRE is a milestone, not full financial independence. Reaching the threshold means your existing investments may compound to the retirement number on their own. You still need income to cover current living expenses until traditional retirement—Coast FIRE removes the pressure to keep saving aggressively for retirement, not the need to earn or spend wisely today.

The model uses a constant real return (after inflation) so both the future target and today's coast number stay in comparable purchasing power. Market volatility, taxes, fees, and spending changes are simplified away.

What affects the result

The coast number is highly sensitive to time horizon and return assumptions because compounding works over many years.

• Retirement spending and withdrawal rate — The future target equals annual spending divided by withdrawal rate. $60,000 at 4% implies a $1.5 million retirement target—the same starting point as the FIRE calculator.
• Years until retirement — More years for compounding lowers today's required balance. A 30-year-old targeting 65 has 35 years; a 40-year-old has 25 years—a materially higher coast number for the same target.
• Real return assumption — A 5% real return produces a lower coast number than 4% because each dollar invested today grows more by retirement. Small return changes move the coast number significantly over long horizons.
• Current invested assets — Compare current balance to the coast threshold to see whether you have already coasted or how much gap remains.
• Taxes and fees — Tax-advantaged growth and low fees help you reach coast sooner; high fees and taxes effectively reduce real return.
• Spending changes — A higher retirement budget raises both the future target and today's coast number. Lifestyle inflation before retirement also affects how much income you still need from work.

Starting early is disproportionately valuable because compounding has more years to work.

Real-world examples

1. Long runway advantage. A 30-year-old targeting $50,000 annual spending at 4% withdrawal ($1.25 million future target) with 35 years to age 65 at 5% real return may need on the order of $225,000–$250,000 invested today to coast—far less than the full FIRE number.

2. Five-year delay cost. Waiting until 35 instead of 30 to start—with the same retirement target and return—raises the required coast balance materially because 5 years of compounding are lost. The gap often exceeds simply saving 5 more years of contributions would suggest.

3. Already coasted. A 38-year-old with $300,000 invested, coast target of $280,000, and 27 years to retirement has crossed Coast FIRE in the model. Current salary still covers rent and groceries; retirement contributions could shift toward other goals if risk tolerance allows.

4. Conservative return stress test. At 4% real return instead of 5%, the same 30-year-old coast number rises noticeably. Running both assumptions shows whether you have margin or are borderline.

Common mistakes

• Confusing Coast FIRE with full financial independence. Coast means retirement may be funded by existing investments; today's bills still require earned income or other assets.
• Assuming a constant return will occur smoothly. Markets vary. A coast number met at a market peak may look different after a downturn without additional contributions.
• Omitting taxes, fees, or major future spending changes. Healthcare, housing, and family obligations can shift the retirement target after you coast.
• Stopping retirement saving without a margin of safety. Continuing contributions after coasting builds buffer for lower returns, earlier retirement, or higher spending.
• Using today's spending as retirement spending without adjustment. Retirement budgets differ from working-age budgets.
• Treating coast as irreversible. Job loss, large withdrawals, or market drops can push you below the threshold again. Revisit annually.

When to use this calculator

Use this calculator when exploring career flexibility—parenting, education, lower-stress work, or semi-retirement—knowing retirement savings may already be on track without aggressive future contributions.

It helps illustrate the value of starting early and shows whether redirecting savings toward near-term goals is reasonable once the coast threshold is met. Pair with the FIRE calculator for the full independence target and timeline, the retirement projection calculator for age-based accumulation views, and the compound interest calculator to isolate growth mechanics.

Revisit when age, spending goals, or portfolio assumptions change.

Related calculators

Estimate the full FIRE target and timeline with the FIRE calculator. Project retirement savings by age with the retirement projection calculator. Explore compound growth mechanics with the compound interest calculator.