InvestToFire Review: The FIRE Calculator That Counts Your Pension

Mikulas  · August 2026 · ~8 min read

I build firenum's Fire Planner, so InvestToFire and I compete for the same audience. That cuts both ways in a review: I know which parts of a calculator are hard to get right, and you should watch me for bias. So here is the conclusion up front. InvestToFire's flagship FIRE calculator does one thing almost every FIRE calculator gets wrong, including several of ours: it subtracts pension, VA, and side income from your FIRE number. For teachers, federal employees, and veterans, that single field is the difference between a $1.5M target and a $1M target. The math checks out. I verified it by hand.

What InvestToFire Is

InvestToFire is a suite of 18 financial calculators at investtofire.com: FIRE number, Coast FIRE, compound interest, dividend income, 401(k), Roth IRA, debt payoff, net worth, a year-by-year withdrawal tax planner, and more. Everything runs in the browser at no charge. There is no signup, no paywall, and no locked tier. The site is run by a solo builder who publishes under the InvestToFire name and funds it with affiliate links, disclosed in the footer.

How I Tested

I ran the three calculators InvestToFire itself considers its strongest: the FIRE calculator, the Coast FIRE calculator, and the withdrawal strategy planner. For each one I recomputed the outputs independently and checked them against the on-screen numbers, down to the dollar. I also poked at edge cases: zero withdrawal rates, pension income larger than expenses, and a 375px phone viewport.

The Pension-Aware FIRE Calculator

The standard FIRE formula is annual expenses divided by your withdrawal rate. Spend $60,000 a year at a 4% withdrawal rate and you need $1.5M. That formula quietly assumes your portfolio covers every dollar of spending, which is false for a large group of people: teachers with state pensions, federal employees under FERS, veterans with VA disability payments, anyone with rental income that will keep flowing.

InvestToFire's FIRE calculator has a field for exactly this. Enter a $20,000 annual pension against $60,000 of expenses and the target drops from $1.5M to $1M, because the portfolio only needs to produce the remaining $40,000. I verified the arithmetic: (60,000 − 20,000) / 0.04 = $1,000,000, and that is what the tool shows. The year-by-year projection table compounds correctly too. I checked row one by hand: $50,000 starting net worth at 7% plus $40,000 of savings lands on $93,500, matching the table.

Edge cases hold up. Set the pension above your expenses and the tool says your FIRE number is $0 and you can retire today, which is the right answer. Set the withdrawal rate to zero and it displays an infinity symbol with a FIRE age of 130. Mathematically honest. A validation message would be friendlier.

Two real caveats. First, the tool assumes the pension pays from the day you retire. Retire at 45 with a FERS pension that starts at 62 and there is a 17-year gap the calculator does not see. Your portfolio has to bridge those years alone, so the true target sits somewhere between the two numbers. If your pension has a start age far from your FIRE age, model it as a dated income stream in a month-by-month planner instead. Second, income entered in that field lowers the target without raising your savings during the accumulation years, so if you meant it as current side income, the years-to-FIRE estimate runs conservative.

The Coast FIRE Calculator

Coast FIRE math is a present value calculation: how much do you need today for compound growth alone to reach your FIRE number by retirement age? Most coast calculators, including firenum's own, discount at whatever nominal return you type in and leave inflation as your problem. InvestToFire's Coast FIRE calculator asks for inflation separately and discounts at the true real return: 1.07 / 1.03 − 1 = 3.883%, the Fisher relation, instead of the sloppy 7 − 3 = 4% shortcut.

I verified it: $1.5M discounted over 35 years at 3.883% is $395,332, and that is the number on screen. That precision is a detail most free calculators skip, and it moves the answer by thousands of dollars over long horizons. Credit where due: on inflation handling, this coast calculator is more rigorous than ours. It also charts the coast trajectory against the keep-saving trajectory and exports the projection to CSV.

The Withdrawal Strategy Tax Planner

This is the most ambitious tool in the suite and the one with no equivalent on firenum. It is a year-by-year spreadsheet for US retirement withdrawals: you type in paycheck income, Social Security, brokerage sales, Roth conversions, and 72(t) distributions for each year, and it computes federal tax, state tax, and after-tax income per row in real time. Qualified and unqualified dividends grow automatically from a starting balance and feed into the tax math.

I tested the engine with a $50,000 annual Roth conversion, single filer. The tool computed $4,024 of federal tax. Working backwards, that is exact progressive-bracket math: a $14,600 standard deduction, 10% on the first $11,600 of taxable income, 12% on the rest. It also stacked the qualified dividends on top of ordinary income and correctly taxed them at 0% because they fell inside the 0% capital gains bracket. This is real tax logic, computed properly.

The catch is in those bracket numbers: $14,600 and $11,600 are the 2024 tax year parameters. For 2026, the standard deduction for a single filer is around $16,100, so the tool overstates federal tax by roughly $200 per year on this scenario. The direction of the error is conservative, your plan looks slightly worse than reality, which is the safer way to be wrong. State tax is a single flat rate you set yourself, a reasonable simplification. If you want a maintained tax engine with current-year brackets, Roth conversion optimization, and state-by-state detail, that is what ProjectionLab's $129/year tier sells. As a no-cost way to see the shape of your withdrawal tax problem, this planner is genuinely useful.

Where It Falls Short

The suite is US-only. Every calculator is denominated in dollars and the tax planner models US federal brackets. If you plan in euros, pounds, rupees, or yen, none of these tools speak your currency.

Nothing persists. Reload the page and your inputs reset to defaults. For a quick calculation that is fine. For a withdrawal plan you spent twenty minutes typing into a 20-row table, losing it to an accidental refresh stings. The CSV export on some calculators softens this.

There is no simulation engine. Every projection uses a single fixed return. There is no Monte Carlo, no historical backtesting, no stress testing, so the output tells you what happens if the market returns exactly 7% every year forever, which it never does. Treat the results as a first estimate, then pressure-test the plan somewhere that models bad sequences.

Google Analytics loads by default, without a consent prompt. Standard practice for a US audience, worth knowing if you care about tracking. Your financial inputs stay in the browser and are not sent anywhere.

InvestToFire at a Glance

Verdict: 4/5

InvestToFire earns its place through correct math and one sharply chosen feature. The pension field alone makes it the right first stop for the millions of people whose retirement is part portfolio, part guaranteed income, an audience most FIRE calculators silently overstate by six figures. The coast calculator is more rigorous about inflation than most of its competition, ours included. The tax planner does real bracket math at a price of zero.

The point comes off for the stale 2024 tax parameters, the lack of persistence, and the single-fixed-return projections. None of these are dealbreakers for what the suite is: fast, correct, single-purpose calculators.

The practical workflow mirrors what InvestToFire's own comparison suggests, and I agree with it. Get your pension-adjusted FIRE number there. Then rebuild the plan as a month-by-month timeline in the Fire Planner, where the pension becomes a dated income stream that starts at 62 instead of a flat deduction, and where you can run the result against every market since 1871. The two tools disagree about almost nothing and cover each other's blind spots.