A common shortcut just subtracts inflation from the nominal return (8% − 3% = 5%), but the exact Fisher equation used here gives a slightly lower number, because inflation also eats into the return itself, not only the principal. The gap between the two grows as either rate rises.

🇵🇹 Rates advertised on Portuguese term deposits and Certificados de Aforro are gross nominal figures — beyond subtracting inflation, interest is also taxed (28% flat, with partial exemptions on some Certificados de Aforro brackets), so the real, after-tax return sits even lower than this calculation alone shows.