Coast FIRE Calculator with Inflation

See how inflation changes the dollar value of your Coast FIRE plan. Compare today's purchasing power with future dollars, review the real return used and verify that both calculation methods produce the same underlying result.

Today's and future dollarsReal and nominal return viewsDouble-count protection

SELECT DOLLAR BASIS VIEW

Changing the view does not create a new financial scenario — it expresses the same modeled plan in today's purchasing power or future nominal dollars.

Inflation Inputs

Current Age

Your age today

Target Retirement Age

When you plan to retire

Annual Retirement Spending in Today's Dollars

Retirement budget in current purchasing power

Expected Nominal Investment Return7.0%

1.0%15.0%

Expected Inflation Rate3.0%

0.0%12.0%

Annual Investment Fees0.10%

0.0%2.0%

Safe Withdrawal Rate4.0%

2.0%8.0%

Base Month & Year

Defines what "today's dollars" means

Inputs

The Inputs That Change Inflation-Adjusted Coast FIRE Results

Inflation affects future spending and the real return available for growth. Nominal return, investment fees, retirement timing, spending and withdrawal rate must use a consistent dollar basis.

Annual Retirement Spending

The yearly retirement budget entered in today's purchasing power.

Inflation

The selected annual rate used to project future spending and convert nominal growth into real growth.

Nominal Return

The modeled annual investment return before inflation is removed.

Investment Fees

Recurring costs that reduce the nominal return available for portfolio growth.

Retirement Timeline

The number of years over which inflation and investment growth are compounded.

Withdrawal Rate

The percentage used to convert annual retirement spending into the full portfolio target.

How To Use

Compare Inflation-Adjusted Coast FIRE in Three Steps

Enter Today's Spending

Enter the annual retirement lifestyle cost expressed in current purchasing power.

Set Growth and Inflation

Enter nominal return, inflation, investment fees and the target retirement age.

Compare Both Dollar Views

Review today-dollar and future-dollar targets, real return and formula reconciliation.

Dollar Basis

Today's Dollars and Future Dollars Describe the Same Plan Differently

Today's dollars preserve current purchasing-power meaning. Future dollars show the nominal amount projected for the retirement year after applying the selected inflation assumption.

Current purchasing power

Today's-Dollar Method

Spending and targets remain expressed in the value of money at the selected base date.

Annual spending$60,000

Retirement target$1,500,000

Coast FIRE number$491,900

Real return3.79%

Retirement-year dollars

Future-Dollar Method

Spending and targets are inflated to the selected retirement year and paired with nominal investment growth.

Future annual spending$145,636

Future retirement target$3,640,894

Present-value Coast #$491,900

Net nominal return6.90%

A larger future-dollar number does not automatically mean the plan has greater purchasing power.

Formula

How Inflation and Fees Change the Real Return

Real return measures modeled portfolio growth after accounting for investment fees and changes in purchasing power.

Real Return Formula (Fisher Equation)

Real Return = (1 + Nominal − Fees) ÷ (1 + Inflation) − 1

Default result3.79% real return

Nominal Return

7.0%

↓ Lower = larger Coast #

Inflation Rate

3.0%

↑ Higher = larger Coast #

Investment Fees

0.10%

↑ Higher = larger Coast #

Real Return

3.79%

↓ Lower = larger Coast #

This calculator uses the exact Fisher equation rather than a simple arithmetic shortcut. The real return is not simply nominal return minus inflation — the multiplicative form accounts for compounding across multiple periods. Learn more about how inflation affects purchasing power (Investor.gov, U.S. SEC).

Result Decoder

Understand Your Inflation-Adjusted Coast FIRE Result

Today-Dollar Coast FIRE Number

The estimated amount required today using spending and growth expressed in current purchasing power.

Future Annual Spending

The annual retirement budget projected into retirement-year dollars using the selected inflation rate.

Future-Dollar Retirement Target

The retirement-year portfolio target associated with the inflated spending amount and withdrawal rate.

Real Return

The modeled purchasing-power growth rate after inflation and investment fees.

Inflation Multiplier

The factor used to convert today's spending into its future-dollar equivalent.

Reconciliation Difference

The difference between the real-method result and the present value of the nominal-method result.

Formula Reconciliation

Why the Real and Nominal Methods Should Match

The real method keeps spending in today's dollars and uses a real return. The nominal method inflates spending and uses nominal growth. When both are implemented consistently, they describe the same underlying present value.

Path A: Today's Dollars

Today's Spending

↓

Today-Dollar Retirement Target

↓

Discount with Real Return

↓

Today-Dollar Coast FIRE Number

Path B: Future Dollars

Inflate Spending

↓

Future-Dollar Retirement Target

↓

Discount with Nominal Return

↓

Present-Value Coast FIRE Number

Result

Same Underlying Present Value

When spending and return assumptions use a consistent dollar basis, the real and nominal methods should reconcile within rounding.

Method A Coast #

$491,900

Method B Coast #

$491,900

Difference

✓ $0

Warning Guide

Avoid Counting Inflation Twice

Future Spending with Real Return

Inflating spending and then discounting with a real return can apply the inflation adjustment twice.

Today's Spending with Nominal Return

Using today's spending directly with nominal growth can understate the target when no inflation conversion occurs elsewhere.

Already-Inflated Input

A future-dollar amount should not be passed through another automatic inflation adjustment.

Use one complete method from beginning to end rather than mixing parts of both methods. The calculator's reconciliation panel shows whether the two approaches are internally consistent for the inputs entered.

Worked Example

One Retirement Goal Shown in Two Dollar Views

The values below are generated from the calculator using consistent inputs. The dollar amounts differ between methods because they use different purchasing-power dates.

Current / retirement age

32 / 62

Annual retirement spending

$60,000

Nominal return

7.0%

Inflation

3.0%

Fees

0.10%

Withdrawal rate

4.0%

Years to retirement

Inflation multiplier

2.43×

Today-Dollar Method (A)

Annual spending (today's $)$60,000

Real return3.79%

Today-dollar target$1,500,000

Coast FIRE number$491,900

Future-Dollar Method (B)

Future annual spending$145,636

Net nominal return6.90%

Future-dollar target$3,640,894

Present-value Coast #$491,900

The displayed dollar amounts differ because they use different purchasing-power dates. After converting them to the same dollar basis, the underlying Coast FIRE result should reconcile within rounding. Reconciliation difference for this example: $0— within the $1 tolerance ✓.

Use Cases

When the Coast FIRE Inflation Calculator Is Useful

You Want Today's-Dollar Results

Use it to keep retirement spending and targets expressed in current purchasing power.

You Want Future Retirement Spending

Use it to estimate the nominal annual spending associated with the selected retirement year.

You Are Comparing Real and Nominal Returns

Use it to see how inflation and fees convert nominal investment growth into real growth.

You Want to Check Your Method

Use the reconciliation panel to identify inconsistent inflation treatment.

You Are Testing Inflation Scenarios

Use it to compare how different inflation assumptions change future-dollar targets and real returns.

You Are Reviewing Another Calculator

Use it to determine whether another result is expressed in today's dollars or future dollars.

Avoid False Precision

Avoid These Inflation Calculation Mistakes

Counting Inflation Twice

Do not inflate spending and then use a real return in the same calculation path.

Mixing Dollar Bases

Do not compare a future-dollar target directly with a today-dollar portfolio amount.

Using Historical CPI as a Forecast

Historical price changes describe the past and do not predict the inflation rate that will occur before retirement.

Ignoring Investment Fees

Fees reduce the modeled nominal return before the purchasing-power result is evaluated.

Using an Arithmetic Shortcut

Subtracting inflation from nominal return is an approximation and may not match the calculator's documented formula.

Treating Future Dollars as Greater Wealth

A larger nominal amount may represent the same purchasing power at a later date.

Assuming One Inflation Rate Is Correct

The selected rate is a planning input rather than a forecast of future prices.

Treating the Result as Advice

The calculator explains formula consistency and does not recommend financial assumptions or decisions.

What This Calculator Does Not Do

Does not forecast inflation

Does not forecast investment returns

Does not calculate personal taxes

Does not model category-specific inflation

Does not recommend a withdrawal rate

Does not run Monte Carlo analysis

Does not provide investment advice

Does not guarantee purchasing power

Official Sources

Verify Inflation and Purchasing-Power Concepts

Use official sources for historical inflation measurements and general investor education. Historical data can explain past purchasing-power changes but does not determine the future inflation assumption used by this calculator.

Bureau of Labor Statistics CPI Inflation Calculator

U.S. Bureau of Labor Statistics

Review historical changes in consumer prices using the official CPI-U inflation calculator.

Role: Historical inflation measurement — not a future inflation forecast

Consumer Price Index: Questions and Answers

U.S. Bureau of Labor Statistics

Review how the Consumer Price Index measures changes in prices paid by consumers.

Role: CPI methodology and measurement context

Investor.gov Educational Resources

U.S. Securities and Exchange Commission

Review official educational information about inflation, investment returns, costs and purchasing power.

Role: General investor education on purchasing power

Review the Calculation Methodology

Coast FIRE Calculator

Review the exact real-return, nominal-return, fee and reconciliation formulas used by this calculator.

Role: Internal methodology and formula documentation

Sources reviewed: July 25, 2026. Official government sources are used for educational context only and do not constitute an endorsement of this calculator.

Inflation and Coast FIRE Questions

How does inflation affect my Coast FIRE number?

Inflation affects the purchasing power of future money and the real investment return used in a today-dollar calculation. Higher inflation generally lowers the real return when the nominal return and fees remain unchanged.

Compare real and nominal return →

What is the difference between today's dollars and future dollars?

Today's dollars express amounts using current purchasing power. Future dollars express the nominal amount projected for a later year after applying the selected inflation assumption.

What is real return?

Real return is the modeled investment growth remaining after accounting for investment fees and inflation. The calculator uses the same documented real-return method as the main Coast FIRE calculator.

Read the Coast FIRE formula →

Should I use today's dollars or future dollars?

Either method can describe the same plan when it is applied consistently. Today's-dollar calculations use real return, while future-dollar calculations inflate spending and use nominal growth.

What does inflation double-counting mean?

Inflation is double-counted when spending is increased into future dollars and the result is also discounted using an inflation-adjusted real return within the same calculation path.

Why is the future retirement target larger?

The future-dollar target is expressed in retirement-year money. A larger nominal amount may represent the same purchasing power as a smaller amount expressed in today's dollars.

Does the calculator predict future inflation?

No. The inflation rate is a user-selected planning assumption. Historical CPI data can provide context but does not forecast the rate that will occur before retirement.

Bureau of Labor Statistics CPI Inflation Calculator →

Why should the real and nominal methods reconcile?

Both methods represent the same spending goal and investment plan in different dollar bases. After converting the results to the same base date, they should match within the documented rounding tolerance.

Review the Coast FIRE calculation methodology →

Methodology and Trust

How This Calculator Handles Inflation

Methodology version: 1.0.0. Last reviewed: July 25, 2026.
Shared calculator-core version: 1.0.0.
Base month and year: defaults to current month and year.
Dollar-basis method: user selects today's dollars or future dollars via toggle.
Real-return formula: ((1 + nominal return − fees) / (1 + inflation)) − 1. Fisher equation.
Net nominal-return formula: 1 + nominal return − fees.
Fee treatment: additive subtraction from nominal return before Fisher equation.
Future-spending formula: todaySpending × (1 + inflation)^years.
Today-dollar target formula: annualSpending / safeWithdrawalRate.
Future-dollar target formula: futureAnnualSpending / safeWithdrawalRate.
Present-value formula: futureDollarTarget / (1 + netNominal)^years.
Reconciliation method: |realCoastNumber − nominalCoastNumber|.
Reconciliation tolerance: within $1 after full-precision calculation.
Compounding frequency: annual (both methods).
Rounding: display only — calculation engine uses full IEEE 754 precision.
Currency locale: en-US.
Official sources reviewed: BLS CPI Calculator, BLS CPI Q&A, Investor.gov (SEC).
Data processing: all calculation runs in the browser. No inputs are stored or transmitted.

Methodology summary

The calculator runs the same retirement plan through a today-dollar method and a future-dollar method. The first uses today's spending and real return; the second uses inflation-adjusted spending and nominal return.

Reconciliation statement

When all inputs use a consistent dollar basis, the present value of the nominal-method result should match the real-method result within the documented rounding tolerance.

Inflation-source statement

Official inflation sources are provided for historical and educational context. The calculator does not use historical CPI data as a forecast of future inflation.

No-advice statement

The calculator does not recommend an inflation rate, investment return, withdrawal rate, retirement age or financial strategy.

Authorship

Methodology maintained by Coast FIRE Calculator.

Disclaimer: This calculator provides educational estimates and formula comparisons. It does not provide investment, tax, legal or retirement advice and does not predict inflation, investment returns or future purchasing power.

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