Coast FIRE LabAbout Coast FIRE Lab
Coast FIRE Lab is a free Coast FIRE calculator built and maintained by one person, Shuping Xu. There is no company behind it, no investor, and no email gate. This page explains why it exists, how the numbers are produced, and how it pays for itself.
Why I built this
In 2021, I sat down to work out my own coast number and opened the first six calculators Google returned. Every one of them asked for my email before showing a result. Two of them gave me a number that ignored Social Security entirely. None of them told me which withdrawal rate they had used, or what inflation assumption sat behind the figure on screen.
The arithmetic itself is not hard. It is three inputs and one exponent. What was missing was a calculator willing to show its work.
It took me five years of my own spreadsheets before I wrote that calculator properly. Coast FIRE Lab launched in 2026. It runs entirely in your browser — nothing you type is sent anywhere, which you can confirm by opening the network tab while you use it. It subtracts Social Security and pensions, because for most people those are the difference between a scary number and a reachable one. And every assumption it ships with is written down on the methodology page, including the cases where those assumptions are wrong.
Who runs it
I'm Shuping Xu. I'm a software engineer, I live in Shenzhen, China, and I have been tracking my own path to financial independence since 2021. Coast FIRE is the version of FIRE that fits my life: I am not trying to stop working in my forties, I am trying to reach the point where I no longer have to save for retirement, so that the work I do afterwards can be chosen rather than required.
I am not a registered investment adviser, a CFP, or a CPA. I do not hold a finance credential and I am not going to pretend otherwise. What I have is the habit of checking a number against its primary source — the IRS notices, the SSA tables, and the original withdrawal-rate research rather than the blog posts that summarise them — and the ability to write the calculator myself, which means every behaviour it has is a decision I can explain rather than one inherited from a library.
How the site makes money
The calculator, the by-age table, and the spreadsheet are free and will stay free.
The paid product is a one-time $15 planner that exports your inputs to a spreadsheet with a year-by-year projection and a scenario comparison. That is the entire revenue model. There is no subscription, no advertising, no affiliate commission, and no lead generation.
Specifically, this site does not:
- sell or share your inputs, because your inputs never leave your browser
- accept payment for placement, ranking, or recommendation of any financial product
- earn commission from any bank, broker, insurer, or advisory firm
- run display ads or affiliate links
If that ever changes, it will be disclosed on this page with a date, and the free calculator will remain free and ungated.
What this site does not do
Coast FIRE Lab does not provide financial, tax, or investment advice. It does not know your tax situation, your health, your family obligations, or your risk tolerance. It cannot tell you what to do; it can only show you what a given set of assumptions implies.
The calculator is a model, and the methodology page lists what the model leaves out: taxes at the account level, health insurance before Medicare, sequence-of-returns risk, required minimum distributions, state taxes, and long-term care. Read that list before you act on any number this site produces.
If your situation involves a pension valuation, a business sale, a divorce, or an estate, you need a professional who can see the whole picture. This site is a starting point for a conversation, not a substitute for it.
How the numbers are produced
Every figure comes from the four inputs you enter and the three assumptions the calculator ships with: a withdrawal rate, a real return, and an inflation rate. The by-age table on the homepage is a separate fixed reference: it uses the same 2.9% real return and 4% withdrawal rate, but fixes retirement at 67, Social Security at $2,084 a month, and three spending levels instead of reading them from your inputs.
Each of these is documented, sourced, and given a stated failure condition on the methodology page. If you find a number on this site you cannot trace to that page, treat it as an error and tell me.
Corrections
I answer correction emails within seven days. When a figure on this site changes because it was wrong, or because the IRS or SSA published a new number, I record what changed and when at the bottom of the affected page rather than editing it quietly.
The IRS publishes its contribution limits in November and the Social Security Administration publishes the following year's COLA in October. I update both figures each year in the month they are released, and the by-age table is re-run whenever either source changes.
If you send a correction and it holds up, I will credit you by name — or keep you anonymous, whichever you prefer.
Contact
I read everything. I am based in Shenzhen, China (UTC+8), so replies may arrive while you are asleep.