Muhammad Tayyab Shabbir

Background

I'm the founder of Avvale Ltd, a London business-planning firm registered in England and Wales (company number 14805382). Since 2021 I have written business plans and built financial models for 500+ founders across the US, UK and UAE. The work is almost entirely projection modelling: revenue build-ups, cash-flow forecasts and multi-decade compound-growth models that investors, banks and grant assessors then pull apart line by line.

Before that I read Theoretical and Mathematical Physics at University College London, graduating with an MSci in 2021. My research work there involved magnetic-field modelling for the European Space Agency's JUICE mission to Jupiter. Physics is where the habit came from: state your assumptions, show the derivation, and let anyone check your arithmetic.

Why I built this site

Compound growth is the same mathematics whether you are modelling a startup's runway or a household's retirement. After years of building the former professionally, I went looking for good tools for the latter and found the free FIRE calculators frustrating: assumptions hidden, formulas undisclosed, tools buried under advertising, and in several cases arithmetic that quietly disagreed with itself between the chart and the table.

So this site takes the opposite position. Every formula is printed on the page next to the tool that uses it. Every assumption, return, inflation, fees, withdrawal rate, is adjustable and defaults to something deliberately middle-of-the-road rather than flattering. Every calculation runs in your browser, so your figures never reach a server. If you can check the maths, you can decide whether to trust the number. If you can't check it, you shouldn't trust it, and that includes trusting mine.

What I am, and what I'm not

Being precise about this matters more on a money website than anywhere else:

• I am a professional financial modeller with a mathematics and physics background, and I build the arithmetic on this site myself.
• I am not a licensed or regulated financial adviser, a CFP, an accountant, or a tax professional. I hold no financial-services qualification and I am not authorised by the FCA, the SEC or any equivalent body.
• This site therefore gives you mathematics and general education, never personal financial advice. It cannot know your tax position, your debts, your health or your risk tolerance. For decisions about your own money, speak to a qualified, fee-only professional in your jurisdiction.

How the numbers are produced

Every calculator on this site runs on one shared engine, so the same inputs always produce the same answer across pages. The core relationships are:

FIRE number = annual spending ÷ withdrawal rate
Coast FIRE number = FIRE number ÷ (1 + real return)^{years to retirement}
real return = nominal return − inflation − fees

Projections compound month by month rather than annually, and every figure is expressed in today's money so you are never comparing a future-inflated number against a present-day budget. The full methodology, including why each default was chosen, is on the about and methodology page.

Corrections

If you find an error in the arithmetic, a broken assumption, or a claim that isn't properly sourced, I want to know and I will fix it and say what changed. Email [email protected] or use the contact page. Verified corrections are made promptly, and material ones are noted on the page.

Elsewhere

• LinkedIn, professional history and current work
• Avvale Ltd, the business-planning firm I founded