Inflation-Indexed Return (IIR) Calculator
Use this calculator to estimate how your investment might grow over time and what that future value is worth after inflation.
What is an IIR calculator?
An IIR calculator helps you estimate your inflation-indexed return—in other words, how much your money grows after accounting for the rising cost of living. A portfolio can look great in nominal terms, but inflation can quietly reduce purchasing power. IIR makes that hidden impact visible.
This page calculates both:
- Nominal future value (what your account statement might show)
- Inflation-adjusted future value (what that money can buy in today’s dollars)
How this iir calculator works
Step 1: Estimate nominal growth
The calculator assumes monthly compounding and monthly contributions. It grows your initial deposit and each monthly contribution at the expected annual return rate.
Step 2: Discount by inflation
After calculating nominal future value, it adjusts that total by your inflation assumption. This produces an estimate of your portfolio’s purchasing power at the end of the time horizon.
Step 3: Compute real annual return (IIR)
The calculator also shows a simplified real annual return using the Fisher-style relationship:
Why inflation-adjusted returns matter
If your portfolio earns 8% while inflation is 3%, your real gain is not 8%—it is closer to 4.85%. Over long periods, that difference dramatically changes retirement projections, withdrawal plans, and savings targets.
- Nominal returns can overstate real wealth growth.
- Inflation assumptions influence your long-term plan as much as return assumptions.
- Small annual differences become large over 10, 20, or 30 years.
Interpreting your results
Nominal Future Value
This is your estimated account value in future dollars. It is useful for comparing with brokerage projections and target account balances.
Inflation-Adjusted Value
This converts future dollars into today’s buying power. If this number is lower than expected, you may need higher contributions, a longer timeline, or more conservative spending assumptions.
Estimated IIR
This is your expected annual real return after inflation. It provides a cleaner basis for long-term planning than nominal return alone.
Example scenario
Suppose you start with $10,000, contribute $500 per month, expect an 8% annual return, assume 3% inflation, and invest for 20 years. Nominal value may appear strong, but the inflation-adjusted value gives a more realistic perspective for financial independence or retirement spending.
Best practices when using an IIR calculator
- Run multiple scenarios (optimistic, base case, conservative).
- Keep inflation assumptions realistic—historical averages can be a helpful guide.
- Review your plan annually as market returns and inflation change.
- Avoid relying on one fixed return assumption for decades.
- Pair this calculator with tax and fee estimates for deeper planning.
Frequently asked questions
Is IIR the same as IRR?
No. IRR (internal rate of return) is a cash-flow based metric often used in project finance and private equity. This calculator uses IIR as an inflation-indexed return concept for personal investing.
Can I use negative return assumptions?
Yes, as long as the value is greater than -100%. This can be useful for stress testing uncertain market environments.
Does this include taxes and fees?
No. Results are pre-tax and pre-fee unless you manually reduce your expected return input to reflect those impacts.