# Stress Testing Guide

Stress testing helps you answer one question: **will my retirement plan still work
if things go wrong?** This guide explains how to use the calculator's built-in stress
tests step by step.

## Why stress test?

A retirement plan is built on assumptions -- about inflation, investment returns, and
how long you will live. If those assumptions turn out to be optimistic, a plan that
looked comfortable can fall short. Stress testing checks the "what ifs" *before* you
retire, so you can adjust while you still have time.

## How to select and run stress tests

1. On the **Results** step, open the **Stress Tests** panel.
2. Tick one or more built-in scenarios, such as **Higher Inflation** or **Longer Life
   Expectancy**.
3. Choose **Run selected** to test the ones you ticked, or **Run all** to test every
   scenario.

Each scenario is applied to a *copy* of your plan. Running a test never changes your
core inputs, so you can experiment freely.

## How to edit a stress test

You can fine-tune any built-in test:

- Open the test you want to change.
- Adjust its parameters and the mode (see below).
- Save your changes.

## How to create a custom stress test

Want to model a risk that is not in the built-in list? Create your own:

1. Choose **Create new test**.
2. Give it a name and a risk category.
3. Add one or more parameters, each with a mode and value.
4. Save and run it like any other test.

## The three parameter modes

Each parameter changes a value in one of three ways:

- **Add** -- shifts a value by an amount (for example, +1% inflation).
- **Set** -- replaces a value with an exact number (for example, 3% returns).
- **Scale** -- multiplies a value by a factor (for example, 1.2x life-expectancy growth).

## How to interpret the results

For every scenario you see how five outcomes changed versus your baseline:

- **Depletion age** -- when your portfolio would run out (blank means it survived).
- **Final portfolio value** -- what remains at the end.
- **Total taxes paid** -- lifetime tax burden.
- **Average tax rate** -- your effective rate.
- **Sustainable withdrawal** -- the income your plan supports.

A **red** value means the scenario hurt that outcome; **green** means it helped.

## Isolated vs stacked runs

- **Run selected / Run all** tests each scenario on its own so you can see its
  individual impact.
- A **stacked** (combined) run applies several tests together to model a worst-case
  "perfect storm".

## How to apply a stress test to your core scenario

When a stress test reveals a change you want to keep permanently -- for example,
retiring a few years later -- use **Apply to core scenario**. This overwrites your
baseline inputs with the stressed values. Use it only when you are sure.

## How to reset a test

If you have edited a built-in test and want the original values back, choose **Reset
to default**. This restores the built-in values for that test. Custom tests you
created are not affected.