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Interest Rate Calculator
What rate are you actually paying? This interest rate calculator works backwards: give it a loan amount, term and monthly payment and it solves the implied annual rate — or hand it a savings goal and it finds the rate that gets you there.
See how this works on a $25,000 loan — 3 real examples
Implied annual rate
0%
Monthly payment
—
Total of payments
—
Total interest
—
Loan balance over time
Amortization schedule at the solved rateYear-by-year breakdown
How we solve for the hidden interest rate
Unlike a payment, an interest rate can’t be isolated with algebra — it sits inside an exponent in the time-value-of-money equation. So both modes use a numeric root-find: the calculator searches for the periodic rate that makes the cash flows balance, then annualizes it (× 12 × 100) into the annual percent you see.
Loan rate: find i so that P = M · (1 − (1 + i)−n) / i
Savings rate: find i so that PV(1 + i)n + PMT · ((1 + i)n − 1)/i = FV
annual rate = i × 12 n = months M/PMT = monthly cash flow
In loan mode the solver returns the annual rate implied by your amount, term and payment; total of payments is payment × months and total interest is that total minus the loan amount. It then amortizes the loan at that solved rate to build the schedule and balance curve. If your payments never total more than the amount borrowed (payment × months ≤ principal), no positive rate can exist — the calculator says so rather than inventing one. Insavings mode it finds the annual rate a starting balance plus monthly deposits needs to reach your target; a negative required rate is a real answer — it means your target is below what you’ll contribute, so you’d only get there by losing money. The rate solved is anominal annual rate; the effective rate (APY) after within-year compounding, or the APR once fees are added, would differ slightly.
Two loan offers and one savings goal
The rate is never printed on the offer. Here it is solved for two ways to finance $25,000 — and once for a $60,000 goal.
Offer one: $500 a month, five years
implied annual rate7.42%
- A $25,000 loan repaid at $500 a month for 60 months hides a 7.42% annual rate.
- The payments total $30,000, so the borrowing itself costs $5,000.
- No paperwork states the rate — it is solved from the three numbers a dealer will actually quote.
The smaller monthly bill in an offer is not the same thing as the cheaper loan — see tab two.
Load this example (opens in a new tab)Offer two: $425 a month, six years
implied annual rate6.90%
- Stretching to 72 months drops the payment by $75 and the rate to 6.90%.
- Total interest rises to $5,600 — the cheaper-looking offer costs $600 more overall.
- Twelve extra months of owing money is what buys the lower rate its friendlier payment.
A lower rate and a higher cost in one offer — the term did that, not generosity.
Load this example (opens in a new tab)In reverse: the rate a goal demands
required annual rate4.24%
- Turning $10,000 plus $300 a month into $60,000 in ten years takes a 4.24% annual return.
- Deposits supply $46,000 of the target; growth must cover the remaining $14,000.
- The solver reads it as a nominal rate — the account’s advertised APY would sit slightly higher.
The same solver runs in reverse: not what a loan charges, but what a goal demands.
Load this example (opens in a new tab)Illustrations only, not financial advice. Your own rate, taxes and insurance will differ — check with a qualified financial advisor before acting on any of this.
Finding the rate behind the numbers, in plain English
- The rate is never stated, so we reverse-engineer it. Give the amount, term and payment on any fixed loan and loan mode returns the annual rate a lender would quote — handy for checking a dealer or store-financing offer.
- Two questions, one tool. Loan mode answers “what rate am I really paying?”; savings-goal mode answers “what return do I need to hit $X?” — the differentiator over loan-only rate calculators.
- Interest rate isn’t APR or APY. The rate here is the nominal figure; APR adds fees on a loan and APY adds compounding on savings, so both sit a little above the plain rate.
- Watch the feasibility line. If total payments barely exceed (or fall below) the amount borrowed, the implied rate is near zero or impossible — a sign the deal is unusual, not that the math is wrong.
- Fixed and monthly. This models a fixed rate with monthly cash flows; variable-rate loans and non-monthly schedules need their own adjustments.
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Frequently asked questions
How do I calculate the interest rate on a loan?
You can’t read it straight off the numbers — the rate is buried inside the payment formula, so this interest rate calculator back-solves it numerically. Enter the amount you borrowed, the fixed monthly payment and the term, and it finds the annual rate that makes those cash flows balance. For example, a $25,000 loan repaid at $500 a month for 5 years implies about a 7.42% annual rate.
What is the difference between APR and interest rate?
The interest rate is the pure cost of borrowing the principal. The APR (annual percentage rate) folds in lender fees, points and some closing costs on top of that rate, so it is usually a little higher and is the better number for comparing loans. This tool solves the nominal interest rate implied by your payments; if your loan had upfront fees, its true APR would be higher than the rate shown here.
What is the difference between APY and interest rate?
On the savings side, the interest rate is the nominal (stated) rate, while APY — annual percentage yield — includes the effect of compounding within the year. A 5% nominal rate compounded monthly is a 5.12% APY. The required rate this calculator returns for a savings goal is a nominal annual rate; the account’s advertised APY would be slightly higher.
What is the difference between a fixed and variable interest rate?
A fixed rate stays the same for the life of the loan, so every payment and the total interest are known up front — that is the case this calculator models. A variable (adjustable) rate moves with an index, so payments can rise or fall over time. Use the solved rate here as the effective fixed rate; a variable loan’s real cost depends on where rates go.
What is a real interest rate?
The real interest rate is the nominal rate minus inflation — it measures your purchasing-power gain rather than the headline number. If a savings account pays a 5% nominal rate and inflation runs 3%, your real return is roughly 2%. This calculator solves nominal rates; subtract your expected inflation to gauge the real rate.
How does my credit score affect the interest rate I get?
Lenders price risk, so a higher credit score generally earns a lower rate and a lower score a higher one — the spread between tiers can be several percentage points, which on a large balance means thousands of dollars. Plug a lender’s quoted payment into loan mode to see the annual rate it really implies, then compare offers on an equal footing.
Disclaimer: these calculators are educational tools, not financial advice. They model your inputs with published formulas, but they cannot know your full situation — for decisions with real stakes, talk to a qualified professional. Formulas and defaults last reviewed .