Interest Rate Calculator

Reverse-calculate the annual compound interest rate needed to grow an initial amount to a final amount over a given period. Free, instant, no signup.

years
Formula: r = (Final / Principal)^(1/years) − 1
  • r = annual interest rate
  • years = investment period

How to use the Interest Rate Calculator

  1. Enter your values. Fill in the fields with your numbers.
  2. Calculate. Press Calculate to run the interest rate calculator.
  3. Use the result. Copy the result or try a related tool next.

Why use our Interest Rate Calculator

Instant results. Enter your figures and the interest rate calculator returns an answer in seconds.
Free & private. Runs in your browser — no signup, and nothing is sent to a server.
Accurate. Uses standard formulas so you can rely on the numbers.

Free to use — premium coming soon

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About the Interest Rate Calculator

The Interest Rate Calculator works backward from the numbers you already know to reveal the one you usually don't: the actual rate on a fixed-payment loan. You enter the amount borrowed, the loan term in years or months, and the fixed monthly payment, and it returns the annual interest rate baked into that deal. It also shows the total of all payments and the total interest you'll pay over the life of the loan, so a string of monthly figures suddenly becomes a single number you can compare against any other offer.

Use it whenever a loan is quoted as a monthly payment instead of a rate. Car dealers, furniture and electronics financing, buy-now-pay-later plans, and some private lenders love to advertise an attractive payment while staying quiet about the rate behind it. By reverse-engineering the rate, you can spot when a 'low monthly payment' is really an expensive loan stretched over extra months. It's equally useful for double-checking a quote you've already received, comparing two financing offers head to head, or sanity-checking a personal loan from a friend or family member.

Behind the scenes, there is no tidy algebra that isolates the rate, because the standard amortization formula, payment equals principal times i times (1 plus i) to the n, divided by (1 plus i) to the n minus 1, can't be rearranged to solve for the monthly rate i directly. Instead the calculator uses iteration: it guesses a rate, computes the payment that rate would produce, compares it to your real payment, and refines the guess (a Newton-Raphson style search) until the two match to a tiny tolerance. The matched monthly rate is multiplied by twelve to give the annual figure you see.

Every calculation runs entirely in your browser, so the loan amounts and payments you type are never uploaded, stored, or shared. The result is the periodic interest rate implied by your inputs, which equals the APR only when the loan carries no separate fees, origination charges, or points; when those exist, the lender's stated APR will be higher. Treat the output as an accurate read on the rate within the payment itself, and round to the nearest hundredth of a percent the way lenders typically quote.

Frequently asked questions

How does this calculator find the interest rate from a monthly payment?

It can't solve for the rate with a single formula, so it iterates: it tries a rate, calculates the payment that rate would generate for your amount and term, then adjusts up or down until that payment matches the one you entered. The matching rate, multiplied by twelve, is your annual interest rate.

What do I need to enter to get a result?

Three things: the loan amount (principal), the loan term, and the fixed monthly payment. With those, the calculator returns the annual interest rate plus your total payments and total interest over the loan.

Is the result the same as APR?

Only if the loan has no extra fees. This tool returns the rate implied by your payment alone, while APR also folds in origination fees, points, and certain closing costs. When those charges exist, the lender's APR will be higher than the rate shown here.

Why would a dealer or lender hide the interest rate?

Quoting only a monthly payment makes a loan feel affordable while obscuring how much it actually costs, often by extending the term. Reverse-engineering the rate lets you compare offers fairly and catch a cheap-sounding payment that hides an expensive rate.

Does it work for simple-interest or interest-only loans?

This calculator assumes a standard amortizing loan with equal fixed payments, which covers most car, personal, and mortgage loans. It is not built for simple-interest payoff math, interest-only loans, or balloon structures, where the payment doesn't fully amortize the balance.

From our blog

How to Evaluate a Pay Raise: From Percentage to Real Take-Home

By the Super Simple Digital Tools Team · Updated June 2026

When a raise lands in your inbox it usually arrives as a single number, either a percentage or a new salary figure, and that lone number hides a lot. The first move is to translate it into the same units you actually spend money in. A 3% bump on $65,000 sounds modest, but it's $1,950 a year, about $162 a month, and roughly $0.94 more an hour. Seeing all four views at once is the difference between a vague 'okay' and a real decision, and it's exactly what a pay raise calculator is built to surface in a single step.

The second step is benchmarking. A raise only means something relative to two things: inflation and the market. With cost-of-living adjustments running around 2 to 3 percent and the 2026 Social Security COLA set at 2.8%, a raise below that range is effectively a pay cut in buying power. Average employer salary budgets for 2026 sit near 3.5%, so anything meaningfully under that may signal you're being undervalued. Use the calculator to express your raise as a clean percentage, then hold it up against these reference points before you celebrate or negotiate.

Third, separate gross from net. The headline number on your offer letter is pre-tax, and a raise can quietly push part of your income into a higher marginal bracket. Only the dollars above the threshold are taxed at the higher rate, so a raise never reduces your overall take-home, but it does mean you keep less of each new dollar than of your base pay. Federal income tax plus Social Security and Medicare alone trim 7.65% off the top before income tax even applies, so plan around the net figure, not the gross.

Fourth, think in compounding terms for anything long-running. Raises stack on top of each other, so the base you start from matters more than any single year's percentage. Two years of 4% beats one year of 5% followed by a flat year, because the second 4% is calculated on an already-higher number. If you're weighing a job change, calculate the new annual figure and project a couple of years forward; a higher starting salary often outruns a slightly bigger one-time percentage at your current employer.

Finally, use the numbers to negotiate concretely. Walking into a review saying 'I'd like more' is weak; saying 'a 6% increase would bring me to $68,900, which aligns with market data for this role' is specific and hard to dismiss. Run the figures first so you can name an exact target salary, an exact percentage, and what it means per paycheck. The calculator removes the mental math, leaving you free to focus on the case you're making rather than the arithmetic behind it.

  • Enter both your current and proposed salary to get the exact raise percentage, then compare it directly against the 2.8% COLA and the ~3.5% average employer budget for 2026.
  • Always read the per-paycheck number, not just the annual one. A $1,800 raise feels large until you see it's about $69 per biweekly check before tax.
  • Estimate your net by keeping roughly 65 to 80 percent of the gross raise, since FICA alone takes 7.65% before income tax is applied.
  • When comparing a salaried offer to an hourly one, divide annual pay by 2,080 to get a true apples-to-apples hourly rate before deciding.

Read the full guide →

Tool by the Super Simple Digital Tools Team. Reviewed by our editorial team. Free to use, no signup required.

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