The nominal rate is the headline number quoted on bonds, savings accounts, and loans before adjusting for inflation. The real rate is what remains after subtracting the erosion of purchasing power, so it measures how much more you can actually buy with the proceeds. Real rates are the figures that matter for long-term wealth and consumption decisions.

The exact Fisher equation multiplies growth factors: (1 + real) × (1 + inflation). Expanding gives nominal = real + inflation + (real × inflation), and the approximation drops that cross-term. With 5% real and 3% inflation the cross-term is only 0.15%, but at 20% inflation and 5% real it grows to 1.0%, and at 50% inflation it dominates the result. Use the exact form whenever inflation exceeds roughly 5%.

TIPS pay a stated real coupon and have their principal adjusted by CPI-U, so their quoted yield is a real rate. The yield gap between a nominal Treasury and a TIPS of the same maturity is called the breakeven inflation rate and reflects the market's expected average inflation over that horizon. Traders use Fisher implicitly: nominal Treasury yield minus TIPS yield approximates expected inflation plus an inflation risk premium.

The Federal Reserve, ECB, Bank of England, and most major central banks target inflation near 2% to anchor expectations. Under Fisher, if the neutral real rate is around 0.5% to 1%, a stable economy should see nominal policy rates settle near 2.5% to 3%. Deviations from that band signal monetary policy is either restrictive (high real rates) or accommodative (low or negative real rates).

Irving Fisher's hypothesis states that real interest rates are determined by real factors like productivity and time preference, while nominal rates adjust one-for-one with expected inflation. Empirically the relationship holds reasonably well over long horizons and across countries, but short-run deviations are common because expected inflation is unobservable and money-illusion frictions delay full pass-through to nominal yields.