CrankyEarl.com

1. Profiles & Accounts Tab

Start here. Enter your age, income, and whatever you've managed to stash away so far — Roth, Traditional, brokerage, high-yield savings, the whole depressing picture. If you have a spouse, there's a tab for them too. Be honest with the numbers. The calculator can't help you if you're lying to it.

2. Assumptions Tab

This is where you tell the calculator how optimistic or delusional you want to be. Set your expected inflation rate, annual income growth, and investment returns — both before and after you stop working. For reference, the S&P 500 has historically averaged around 10% annually before inflation, and most diversified 401(k) portfolios tend to land somewhere between 5% and 8% depending on your mix. Use those as a reality check, not a guarantee. The market doesn't care about your retirement date.

3. One-Time Events

Also in the Assumptions tab. Got a windfall coming? A big purchase on the horizon? An inheritance you're too polite to mention at Thanksgiving? Model it here. Enter the amounts, what type of account it lands in, and the age you expect it to happen. The calculator will fold it into your projections without judgment.

4. Expenses Tab

What's retirement actually going to cost you? Enter your expected monthly expenses in today's dollars — not some fantasy number, your real number. If you're retiring within the next 10 years, this is worth some genuine soul searching. Your life in retirement probably looks different than your life today. Kids at home now but not then? That changes a lot — food, insurance, the second car, the chaos budget. Think forward, not backward. Check the box if you want the calculator to inflate those expenses between now and retirement, which, by the way, you should, because everything gets more expensive. Always.

5. Viewing the Projections

Change a number on the left, watch the charts react on the right. The top chart shows your pile growing (or not) over time. The bottom section walks through your retirement year by year — withdrawals, income, taxes, inherited accounts burning down under the 10-year rule. It's a lot of information. That's the point.

6. Monte Carlo Simulation

When you think you've got a solid plan, hit "Run Monte Carlo Simulation." It'll open a new tab and throw your numbers against 10,000 different randomly sampled sequences of real S&P 500 monthly returns going back to 1928. Good decades, bad decades, crashes, booms — all of it. The result is a Success Rate: the percentage of those 10,000 scenarios where your money lasted. If it's high, sleep well. If it's not, come back and adjust.

A few things worth knowing: the simulation uses your actual monthly expenses — not a withdrawal rate percentage — because in real life your grocery bill doesn't care what the market did last year. Run it a few times and you'll notice the results are slightly different each time. That's not a bug, that's statistics working correctly. Small variation means 10,000 simulations is doing its job. If the number swung wildly between runs, you'd have a problem.

The simulation also has a Market Crash Stress Test you can enable in the settings panel. You pick the retirement year the crash hits, how severe it is (as a percentage portfolio drop), and how many years the market stagnates afterward. During that stagnation window, market-exposed accounts earn roughly 2% per year — dividend yield only, no price appreciation — before historical returns resume. This models a "lost decade" scenario: a crash followed by a prolonged sideways market, which is the scenario most likely to derail a retirement that looks fine on paper. If your plan survives that, it's actually stress-tested. If it doesn't, better to know now.

7. Load an Example

Not sure where to start, or just want to see the calculator in action? Hit the green "Load Example" button in the nav. There are five pre-built scenarios — a classic 401(k) saver, a FIRE-focused single, a late starter, a coordinated couple, and an aggressive young saver. Load one, poke around, change numbers, and see what happens. They're realistic, not perfect — because nobody's situation is perfect. Use them as a starting point, not a blueprint.