How the numbers on this site are worked out

Every projection on this site grows money at 8% a year. That is a planning assumption, not a forecast, and it is labelled that way wherever it appears.

Contributions are compounded quarterly, not yearly. A euro invested in January should not sit idle until December, and quarterly is closer to how a monthly standing order behaves than an annual step.

8% is before inflation. If you want the number in today's money, run it nearer 5%. The savings-rate chart in the book does exactly that, which is why its years look longer than the calculator's.

To turn a pot into an income, the site divides annual spending by 4%. That is the figure most financial-independence maths uses, and it comes from US research on 30-year retirements.

It is a rule of thumb and it has real critics. It assumes a long horizon, a stock-heavy portfolio and US tax treatment. Read it as a benchmark that lets two plans be compared, not as a promise about your own money.

The site argues you should aim at a monthly income rather than a total. The book makes that case in full. The 4% figure is only how a total gets turned into a monthly number so the two can be compared.

The calculator models employee contributions, employer contributions, income tax bands, personal allowances, tax credits, regional surcharges and filing status for 22 countries, 19 of them in Europe. All amounts are monthly and in local currency.

It is built for planning and for comparing one country with another. It is not a payroll engine. It will not match your payslip to the cent, and it does not know about your pension scheme, your benefits, your student loan or your local rate.

Rates track 2026 rules as published by each country's tax authority. Where a rate is capped, banded or split between employer and employee, the model follows the same structure rather than flattening it to a single percentage. That is the whole point: the flat percentages you see quoted elsewhere hide exactly the effects that decide what reaches your account.

Countries covered: Germany, Estonia, Latvia, Lithuania, Poland, Ireland, United Kingdom, Finland, Sweden, Netherlands, France, Spain, Portugal, Italy, Denmark, Norway, Greece, Romania, Belgium, plus the United States, Canada and Mexico.

The payslip. €8,501.29 of employer cost, €6,353.73 gross, €5,000.00 net. Estonia. Taken from a public Estonian salary calculator and kept as a screenshot.

The portfolio. It produces roughly €16,000 a month. 60.4% of it is money I put in, 27.6% is growth, and the rest is a flat sale, a pension and share options. The total is in the book, not on this site: it is the least useful number I could give you and the easiest one to argue about.

The return. More than an index fund, blended across everything I own over ten years. Most of it comes from financing property flips, which is nearer to a business than to investing. It carries risk an index fund does not, and you should not plan around it.

The career. Fifteen years in sales. €700 a month at the start. €243,000 in my best year against a €50,000 base. First of more than 250 account executives globally at Deel in the first half of 2023.

Figures that are not mine are attributed on the page that uses them, with the source named and the date it was published. If a study is US-only, the page says so, because most personal-finance research is and most of it does not transfer to Europe.

Where something is contested, the site says it is contested rather than picking the convenient side.

Every number that appears in the book, the guides and this site is held in one file and checked before anything is published. A figure that changes gets changed everywhere, not in the one place somebody remembered.

If you find a number that is wrong, email nikita@9-5fastlane.com. The date at the top of this page changes when the page does.

The limits of all of it are set out in what this is and what it is not.