Question: My investment in India earns 8% a year, and inflation is running at 5%. Everyone says "just subtract" to get the real return of 3%. Is that mathematically exact, or is there a more precise way to calculate it — and how different is the answer?
Answer: The simple subtraction gives 3%; the exact (Fisher) real return is approximately 2.86% — the simple method slightly overstates the real return.

Supporting evidence:
title: Inline formula / method note
quote: Fisher equation (exact) vs. simple nominal-minus-inflation approximation — standard economics/finance formula
context: Fisher equation (exact) vs. simple nominal-minus-inflation approximation — standard economics/finance formula.