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Compound interest and FIRE calculator.

Move the sliders and watch a portfolio compound year by year, with contributions and interest side by side. Every number updates as you go, the full chart and table sit right below, and any calculation is one link away from a friend.

Want the year you reach FI, and how long the money lasts? That is what the app is for.

Portfolio · Details ›
Passive income /mo
Start
Contributions
Interest
Projection details

Year by year

Portfolio
This yearSo far
Start·
Contributions
Interest

Tap or drag across the chart to pick a year.

YearPortfolioContributionsInterest

Assumptions: annual compounding, deposits at the end of each month, no inflation, passive income at a 4% withdrawal rate. The same defaults as the app.

The app

Three questions. Three calculators. One app.

The calculator above is one of three in simpleFIRE. The app adds the two questions that come next, when you reach your target and how long the money lasts once you live off it, tests every plan with Monte Carlo or against real market history, and then shows every number behind the answer: the chart you tap through year by year, the table, the assumptions.

Projection calculator: result card with portfolio value and passive income, sliders below
What will it grow into?

Projection

Starting portfolio, monthly contribution, period and annual return. Watch the portfolio compound year by year, with your contributions and the interest they earned side by side.

Time to FI calculator: years to target with the FI date and passive income
When do I get there?

Time to FI

Set your FI target and see the year and month you reach it, the passive income it pays, and how far along you are each year. Not sure of your number? The app estimates it from what you spend.

Drawdown calculator: how long the portfolio lasts and when it runs out
How long will it last?

Drawdown

Start taking money out. See the year and month the portfolio runs dry, how much you withdraw along the way, and whether the returns outrun your withdrawals.

Monte Carlo and Historical

Three methods. Your choice.

Markets never pay the same return twice. Switch any of the three calculators to Monte Carlo and the app runs 5,000 simulations of your exact plan, updated live as you move a slider. Prefer real data? Historical backtests your plan the way the Trinity study tested the 4% rule: through every period of real S&P 500 and US Treasury returns, with the inflation each year actually brought. Or keep it simple with a fixed rate. Set your mix of stocks and bonds with one slider and read every answer as a plain chance.

Projection with Monte Carlo: the portfolio you have with a 90% chance
Projection details with Monte Carlo: the chance of having at least each amount

Projection

Monte Carlo: the portfolio you have with a 90% chance, and the chance of having at least each amount.

Time to FI with Historical: when you reach your target with a 90% chance
Time to FI details with Historical: the chance of reaching your target by each year

Time to FI

Historical: when you reach your target with a 90% chance, and the chance of getting there by each year.

Drawdown with Historical: how long the money lasts with a 90% chance
Drawdown details with Historical: the chance your portfolio lasts through each year

Drawdown

Historical: how long your money lasts with a 90% chance, and the chance it lasts through your planning horizon.

Method settings: Fixed rate, Monte Carlo or Historical, and one slider for the mix of S&P 500 stocks and US Treasury bonds

Your method, your mix

Fixed rate, Monte Carlo or Historical, and one slider for S&P 500 stocks and US Treasury bonds.

Everything in the app

Every number, explained.

The result is one tap from the year-by-year story behind it, and every assumption is a slider you can see and change.

Tap through the years

Drag a finger across the chart and the result above it follows, year by year. Let go and it returns to your answer.

Today's money or nominal

Inflation is one tap away on every calculator. Flip any result between what it buys today and what your account will show, while your FI target and your withdrawals keep up with prices.

Share it as a PDF or a picture

A clean one-page report with the chart, the assumptions and the yearly table, or an image made for messages and social media.

Saved profiles

Keep several plans, a cautious one and a bold one, and switch between them in a tap.

Your assumptions, your rules

Compounding, contribution timing and yearly increases, withdrawal timing and rate, planning horizon, your stocks and bonds mix, the chance you plan with: every setting sits next to the result it changes, every result lists the ones it depends on, and the About page explains how every number is calculated.

Milestones on the chart

The year interest overtakes your deposits, the line of your FI target, the year the money runs out: marked where they happen. With Monte Carlo and Historical, the chance of your plan working, bar by bar.

Dark, light, and yours

Two themes, your currency and number format, text that follows your accessibility settings.

iPhone, iPad and Mac

One app across all your Apple devices, with Split View and Slide Over on iPad.

Private by design

No account, no sign-in, no tracking. Your numbers never leave your device. Privacy policy.

Get simpleFIRE for iPhone, iPad and Mac.

Everything on this page, plus Time to FI, Drawdown, Monte Carlo and Historical, in your pocket.

Blog

The magic of compounding.

All posts
The 4% rule, tested on 59 start years.It lasted forty years in 54 of them. Ten years of waiting costs $651,000.Same deposits, same return, one decade later. In year 11, your money starts out-earning you.When interest quietly overtakes your deposits.
What's new

Version 2.3.1

Full changelog
2.3.1
October 8, 2026
  • Rate simpleFIRE in one tap: a new row in the app's settings opens the App Store review page. Every review helps other FIRE planners find the app.

Take the calculator with you.

simpleFIRE for iPhone, iPad and Mac. Your numbers stay on your device.