Coast FIRE LabShuping Xu
Shuping Xu is the founder of Coast FIRE Lab, a free Coast FIRE calculator that subtracts Social Security and pensions and documents every assumption it ships with. It launched in 2026, after a search for a calculator that would show its work without asking for an email first turned up nothing.
Background
I am a software engineer. That is where the habit of checking a number against its primary source comes from — not from a finance credential. I do not hold a CFP, CFA, or CPA designation, and I am not a registered investment adviser.
What I do have is narrower and more specific: I have been running my own retirement numbers since 2021, I have read the original withdrawal-rate research rather than the blog posts summarising it, and I wrote the arithmetic behind every calculator on this site myself — which means I can explain each line of it instead of trusting a library to be right.
Why I write about Coast FIRE
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 whatever work comes afterwards can be chosen rather than required. That distinction is what this site is built around.
The first time I calculated my own coast number, two calculators gave me two answers that differed by six figures, and neither page explained why. One had ignored Social Security entirely. The other had used a nominal return rate where a real one belonged. Neither stated its withdrawal rate. I could not tell whether the gap came from my inputs or from their assumptions, and that is a design failure rather than a knowledge gap.
So I write the way I wanted those pages written: state the assumption, cite the source, and name the condition under which the assumption stops being true. The methodology page is the long-form version of that commitment, including a section on the cases where my own defaults would be the wrong choice.
What I'm responsible for
I wrote and maintain every page on this site. Currently that means:
- The Coast FIRE calculator on the homepage, including how it handles Social Security, pensions, and inflation
- The Coast FIRE number by age reference table, and the fixed assumptions behind it
- The methodology page, which sources every default the calculator ships with
- The About page, including the disclosure of how this site is funded
Every figure on this site should trace back to a documented assumption on the methodology page. If you find one that does not, that is an error and I want to hear about it.
How I keep this accurate
Tax and benefit figures change every year. I update the IRS contribution limits in November, when the agency publishes the following year's numbers, and I re-check the Social Security figures against SSA's own publications rather than news summaries — the $2,084 monthly average this site uses is the retired-worker figure in the OASDI fact sheet dated 30 June 2026. The by-age table is re-run whenever either source changes.
When a figure changes, the page carrying it gets a new "last updated" date, and the methodology page records what changed and when. Corrections that come from readers are credited — by name, or anonymously if you prefer.
I answer correction emails within seven days.
Contact
I am based in Shenzhen, China (UTC+8), so replies may arrive while you are asleep.