8 free calculators for FIRE planning, retirement projections, compound growth, and the hidden costs that quietly eat returns.
Retirement planning sounds complicated, but it really comes down to three numbers: how much you need (your FIRE number), how fast your money grows (your rate of return, net of fees), and how much time it has to compound. Every calculator in this hub answers a question about one of those three.
The 25x-expenses FIRE number comes from the 1998 Trinity Study, which tested historical market data to find a withdrawal rate unlikely to deplete a portfolio over a 30-year retirement — commonly cited as ~4% annually, i.e. 25x expenses. The U.S. Securities and Exchange Commission's investor.gov tools and S&P Dow Jones Indices' SPIVA reports ground the fee and index-fund comparisons in this hub.
The single most important variable most people underestimate is time. The Compound Interest: Early vs Late calculator exists specifically to make that gap visible.
| Calculator | What it answers | Best for |
|---|---|---|
| FIRE Number | How much you need invested to retire on your terms | Anyone planning early retirement |
| Retirement Wealth Estimator | Projected portfolio value at retirement age | Long-range retirement planning |
| Compound Interest: Early vs Late | The cost of delaying investing by N years | Anyone weighing "start now vs later" |
| 401(k) Contribution | Growth impact of contribution % and employer match | Employees with a 401(k) |
| Investment Fee Drag | Lifetime cost of high expense ratios | Anyone comparing fund fees |
| Index Fund vs Stock Picking | Outcome comparison between passive and active investing | New investors choosing a strategy |
| Inflation & Savings Erosion | How inflation erodes uninvested cash over time | Anyone holding large cash balances |
| Side Hustle Investment Value | What side income becomes if invested instead of spent | Freelancers and side-hustlers |