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About This Site

Who built this

My name is James. I'm a software developer, and I built Investment-Calculator.com because I kept running into the same problem: every financial calculator I found online was either buried in ads, required a sign-up, or didn't show its work. I wanted tools that were fast, transparent about the math, and didn't come with strings attached.

I'm not a financial advisor or a licensed investment professional. What I do bring is a developer's instinct for accuracy: every calculator on this site uses the standard financial formulas that textbooks and professional tools use, and each page documents those formulas and links to authoritative sources so you can verify the methodology yourself.

What this site is

Investment-Calculator.com is a collection of 8 free financial calculators covering the most common personal finance calculations: compound interest, return on investment, dollar cost averaging, loan payments, retirement planning, inflation impact, stock profit and loss, and FIRE number.

Every calculator runs entirely in your browser. Nothing you enter is sent to a server or stored. The site uses anonymous analytics to count visits and which calculators are used; the numbers you type are never included. The privacy policy has the detail. There are no accounts, no paywalls, and no ads. The site exists to give anyone a fast, honest answer to a financial question.

How we ensure accuracy

Each calculator is built on established financial formulas, the same ones used in textbooks, spreadsheets, and professional financial software. The compound interest calculator uses A = P(1 + r/n)nt. The loan payment calculator uses the standard amortization formula. The retirement planner uses the future value of an annuity. None of these are proprietary or invented; they are standard, well-documented methods.

Each calculator page includes a methodology note that names the formula, defines its variables, and links to an authoritative external source: the Federal Reserve, the Bureau of Labor Statistics, the CFPB, the IRS, or the academic research the withdrawal rates are drawn from. If a number doesn't look right, the methodology note is the starting point for checking the math.

If you find an error in a calculation, email contact@investment-calculator.com and it will be corrected. Getting the numbers right is the whole point.

How the numbers are checked

On October 10, 2026 the default example on every calculator was run through an outside calculator, and every figure quoted in the text of a page was recomputed from the calculator on that page.

  • Compound interest and inflation: the SEC's compound interest calculator on Investor.gov returns the same figures: $22,196.40 for $10,000 at 8% for 10 years compounded monthly, and $18,061.11 for $10,000 growing at 3% for 20 years.
  • Dollar cost averaging, the home page calculator, retirement and FIRE: these add a monthly contribution. Investor.gov assumes each contribution is made at the end of the month; this site assumes the start of the month, which gives each contribution one more month of growth. With Investor.gov's timing our formulas return its figures to the cent ($379,684.42 for $500 a month at 10% for 20 years). With ours the result is $382,848, about 0.8% higher.
  • Retirement, monthly saving needed: Investor.gov's savings goal calculator gives $476.35 a month for the default plan with contributions at the end of each month. This site gives $474 with contributions at the start.
  • Loan payment: calculator.net returns the same $1,580.17 a month and $318,861 in total interest for $250,000 at 6.5% over 30 years.
  • ROI: calculator.net returns the same 50% total and 14.47% a year for $10,000 growing to $15,000 over 3 years.
  • Stock profit and loss: plain arithmetic, checked by hand.

What this site is not

The results from these calculators are projections based on the inputs you provide and the assumptions built into each formula. They are for planning and educational purposes only.

  • We are not a registered investment advisor and do not provide personalized financial advice.
  • Calculator results do not account for taxes, fees, inflation adjustments (unless explicitly modeled), or individual circumstances.
  • Past market returns used as default inputs are historical averages and do not guarantee future results.
  • Nothing on this site should be taken as a recommendation to buy or sell any security or take any specific financial action.

For decisions involving significant amounts of money, consult a qualified financial advisor or certified financial planner who can account for your full financial picture.

Methodology references

The following external sources inform the default assumptions and formula implementations used across the calculators:

Investment-Calculator.com is an independent site. It is not affiliated with any financial institution, brokerage, or investment product. Results are for informational purposes only and do not constitute financial, tax, or legal advice.