Coast FIRE Calculator
Enter your target at retirement, your ages, current investments and expected real return. The calculator gives the coast number: the sum that, invested today and left alone, reaches your target purely by compounding - after which new saving becomes optional.
Coast calculators usually bury the sensitivity. This one shows the same target at your rate and at 7%, because the gap between them is the real lesson: return assumptions dominate the early decades more than any salary raise.
How to use
- Set the retirement target from your FIRE number, not a round million.
- Enter current age and retirement age honestly - the multiple shown is what compounding promises at your rate.
- Compare the figure with what you hold today; the surplus or deficit is the whole conversation.
Frequently asked questions
What is Coast FIRE?
The point where invested savings alone, left to compound, reach your retirement target by your target age. Past it, salary only needs to cover living costs - pension contributions become optional, and career decisions get much braver.
How is the coast number calculated?
Pure discounting: target divided by (1 + real return) to the power of years remaining. A million needed at 65 for a 30-year-old at 5% real is about 209k today - the multiple shown is compounding's whole promise.
Why does the return assumption matter so much?
Because it is exponentiated over decades: at 35 years to retirement, 5% versus 7% real nearly doubles the required starting sum. Costs, diversification and staying invested move this assumption more than any stock pick.
Is Coast FIRE risky?
The risk is front-loaded: you stop saving on a promise about forty future years of returns. Mitigations - keep the target conservative, revisit annually, and treat coast as savings-optional rather than savings-impossible. A crash at 60 hits regardless; coast just changes what you do at 35.