EDDYMENS

Tutorials

The Portfolio Runway Calculator

Table of contents

Overview

The Portfolio Runway Calculator [↗] is a simulation tool that models how investment portfolio evolves over time when withdrawals, deposits, investment returns, and inflation are applied year-by-year.

The calculator allows you to:

  • Simulate withdrawals and contributions
  • Model different annual returns
  • Compare best and worst return scenarios
  • View both nominal and inflation-adjusted balances
  • Track when a portfolio becomes depleted

Core Model

Each year the portfolio balance is updated using the following sequence:

  • Apply investment growth
  • Substract withdrawals
  • Add deposits
  • Calculate the inflation-adjusted value

The portfolio never goes below zero

If the calculated balance becomes negative, the tool marks the portfolio as DEPLETED.

Input Configuration

Starting Balance

The starting value of the portfolio

Example

01: 1,000,000

This is the base value used to calculate:

  • Yearly growth
  • Depletion thresholds
  • Visual health indicators

Base Return (per year)

Expected annual return.

Example

01: 8%

This value is used as:

  • The default return for all years
  • The baseline for scenario comparisons

Individual years can override this value.

Inflation Rate (per year)

Annual inflation used to calcualte real purchasing power

Example

01: 3%

Inflation affects:

  • Real (inflation-adjusted) portfolio balance
  • Inflation adjustments applied to seeded withdrawals and deplosits.
  • The displayed real return

Currency

The currency selector changes the display symbol used throughout the interface.

Examples include:

  • USD ($)

  • EUR (€)

  • GBP (£)

  • GHS (₵)

  • NGN (₦)

  • CAD (C$)

  • AUD (A$)

This setting does not affect calculations.

Running the Simulation

Click Run to start the simulation.

This creates the first simulation year and reveals:

  • The yearly table
  • The scenario comparison panel
  • Summary metrics

You can then add more years using + Add Year.

Year-by-Year Table

Each row represents one year of the simulation.

Columns include:

  • Withdrawal: Money removed from the portfolio.
  • Deposit: Money added to the portfolio.
  • Return: Annual investment return for that year.
  • End Balance (Nominal): Portfolio value at end of year
  • End Balance (Real): Inflation-adjusted value
  • Growth: Value created by investment return

Important Notes

The calculator is designed for scenario exploration, not prediction.

Investment returns, inflation, and withdrawals in the real world will vary.

Use the tool to explore questions such as:

  • How long will my portfolio last?

  • What happens if returns are lower than expected?

  • How do withdrawals interact with inflation?

  • How much difference do additional deposits make?