Coast FIRE Calculator
The Coast FIRE calculator works out the single number that matters for a coast plan: how much you need invested today so that compounding alone can carry you to your target corpus by retirement.
What this calculator does
Enter a few assumptions and the calculator tells you your coast number — the portfolio value you need today to reach your retirement target with no further contributions. It also works in reverse: given your current savings, it can estimate how many years of growth remain before you coast. The idea is to make the compounding maths concrete, so you can see whether you are already coast-ready or how far short you stand. If you are new to the idea, our Coast FIRE explainer covers the concept in plain language first.
The calculator does not give you a spending plan, an asset allocation or a withdrawal strategy. It answers one focused question — is your portfolio already on track to grow into the target you need — and leaves the surrounding planning to you.
Inputs you'll need
Five inputs drive the result: your current age, the age you expect to retire, your target corpus at retirement, the annual return you expect on your investments, and an inflation assumption if you want the target expressed in today's money. Your target corpus is usually your expected annual retirement spending multiplied by a withdrawal factor — many planners use 25×, following the 4% rule. A rough estimate is fine; you can refine it as your plan matures.
How the calculation works
The coast number is the present value of your target corpus, computed as target corpus ÷ (1 + expected return) ^ (years to retirement). The exponent does the heavy lifting: it discounts the target back to today at your assumed growth rate over the remaining years. Because the formula compounds, small changes in the return or the time horizon have an outsized effect on the result. The calculation assumes you make no new contributions from today onwards — that is what coast means — and that returns arrive steadily rather than in market-sized lumps.
A worked example
For illustration: imagine you are 30, want to retire at 55 with a ₹5 crore corpus, and assume a 10% annual return. That gives 25 years of growth. Your coast number is roughly ₹5 crore ÷ (1.10)^25 ≈ ₹46 lakh. In this hypothetical, if you had about ₹46 lakh invested today and it compounded at 10% a year with no further deposits, it would reach around ₹5 crore by the time you turn 55. Choose a more cautious 8% return and the same goal needs roughly ₹73 lakh. All figures here are illustrative — substitute your own assumptions.
What the results mean
The output is a single number plus some context: how close your current savings are to the coast target, and how much longer the runway would be if you fell short. Being at or above the number means compounding can handle the retirement corpus and your contributions become optional. Being below it means you still need growth time, additional savings, or both. The result is not a retirement date — it is a check on whether your portfolio is on autopilot yet.
Assumptions and limitations
The calculator assumes a constant return on your investments, steady inflation and no contributions after today. Real portfolios bounce around, and the order of good and bad years — sequence-of-returns risk — can matter as much as the average return. Inflation also silently shrinks what a fixed rupee target can buy, so review both the return and inflation assumptions over time. For a harder stress test, run the same plan through a Monte Carlo simulation, which models hundreds of possible return paths instead of one smooth average.
Estimates, not guarantees. A coast number is a projection built from the assumptions you supply. Market returns are not steady or guaranteed, so treat the result as a planning guide — and for real money decisions, consider professional advice.
Frequently Asked Questions
What is a coast number?
Your coast number is the amount you need invested today so that, growing at your expected return until your target retirement age, it reaches your full retirement corpus with no further contributions.
What return should I assume?
Use a figure that matches your actual asset mix. For a long-horizon, equity-heavy portfolio many planners assume between 8% and 12% a year, but returns are uncertain — testing a lower, conservative rate as well is wise.
Should inflation change my coast number?
Yes. If your target corpus is expressed in today's money, your coast number is lower than if you inflate the target to its future value. Pick one consistent approach and state it explicitly.
Is reaching Coast FIRE enough?
Only for the retirement portfolio. Coast FIRE does not fund your living costs before retirement, so you still need an income for day-to-day expenses. It also assumes the returns you planned for actually arrive.
Does it work for Indian investors?
Yes. The maths is the same whether amounts are in rupees, and Indian savers typically blend equity SIPs with EPF, PPF and NPS. Keep return assumptions realistic and remember taxes are not modelled.