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Interest Rate Calculator
Know the loan amount, the payment and the number of payments but not the rate? Enter them to solve the interest rate (APR), the effective annual rate and the total interest, with each step of the calculation shown.
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$
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Optional final lump sum (e.g. a lease residual). 0 if none.
Enter your values to see the result.
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How to use the Interest Rate Calculator
- Enter the loan amount you borrow (or the amount you actually receive after fees).
- Enter the payment and the term in months or years.
- Choose the payment frequency and any balloon or residual due at the end.
- Press Solve to get the interest rate, effective annual rate and total interest.
- Check the Newton iterations and schedule to see how the answer was found.
How the interest rate is solved
For a fixed-payment loan, the amount borrowed equals the present value of all payments:
L = P × (1 − (1 + i)−n) ÷ i + B × (1 + i)−n
where L is the loan amount, P the payment, n the number of payments, B an optional final balloon and i the rate per period. There is no algebraic formula for i, so the calculator uses Newton's method: start with a guess, then repeatedly improve it with inew = i − f(i) ÷ f′(i), where f(i) is the present value minus L. It usually converges to many decimal places in 3 to 6 steps (a bisection search is used as a fallback).
The APR is i × payments per year. The effective annual rate (APY) also counts compounding: (1 + i)payments per year − 1.
Examples: rate implied by a payment
| Amount | Monthly payment | Payments | Total interest | APR |
|---|---|---|---|---|
| $25,000 | $495.00 | 60 | $4,700 | 7.00% |
| $10,000 | $320.00 | 36 | $1,520 | 9.43% |
| $5,000 | $175.00 | 36 | $1,300 | 15.68% |
| $300,000 | $1,996.00 | 360 | $418,560 | 7.00% |
| $40,000 | $650.00 | 72 | $6,800 | 5.31% |
If a lender quotes only a payment and a term, use this to check the real rate. If fees are deducted from the amount you receive, enter the net amount instead to see the rate including fees.
Frequently asked questions
How do I find the interest rate on a loan from the payment?
Solve L = P × (1 − (1 + i)^−n) ÷ i for the periodic rate i, then multiply by the number of payments per year. There is no closed formula, so it is solved numerically. For example, $25,000 repaid at $495 a month for 60 months is an APR of about 7.00%.
What is Newton's method?
It is a fast way to find the root of an equation. Starting from a guess, each step moves to where the tangent line crosses zero: i_new = i − f(i) ÷ f'(i). For loan rates it typically reaches full precision in a few steps.
What is the difference between APR and APY?
APR is the periodic rate times the number of periods per year. APY, or the effective annual rate, includes compounding: (1 + i)^periods − 1. A 7% APR with monthly payments is about a 7.23% effective annual rate.
Why does it say the rate would be negative?
If the payments add up to less than the amount borrowed, no positive interest rate fits. Check that the payment, the term and its unit are correct.
Can I include loan fees?
Yes. Enter the amount you actually receive after fees as the loan amount, keeping the same payment. The solved rate is then close to an APR that includes those fees.
Does this work for leases?
Yes. Enter the vehicle's capitalized cost as the amount, the monthly payment, the term and the residual value as the balloon to estimate the implied rate. Leases are often quoted as a money factor; multiply it by 2,400 to get an approximate APR.
Is my data private?
Yes. The calculation runs entirely in your browser.
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buys, plus how many shares to buy to reach a target average.Position Size CalculatorHow many shares or units to trade so a stop-loss risks only a set share of your account.P/E Ratio CalculatorPrice-to-earnings ratio, earnings yield and PEG ratio from share price, EPS and growth.EPS CalculatorBasic and diluted earnings per share from net income, preferred dividends and share count.WACC CalculatorWeighted average cost of capital from equity, debt, their costs and the tax rate.CAPM CalculatorExpected return from the risk-free rate, beta and market return using the CAPM formula.Payback Period CalculatorPayback and discounted payback period for an investment with even or uneven cash flows.Effective Annual Rate CalculatorConvert a nominal rate to the effective annual rate (EAR / APY) for any compounding, or back.Dividend Reinvestment CalculatorProject a DRIP: portfolio value, shares and income with and without reinvesting dividends.Credit Card Payoff CalculatorSee when your card is paid off, the interest you pay, and how it compares with the minimum.Debt Snowball CalculatorPlan payoff of several debts: snowball vs. avalanche order, debt-free date and interest saved.College Savings CalculatorProject future college costs and see how much you need to save each month to pay for them.Retirement Withdrawal CalculatorSee how many years your retirement savings last with withdrawals, returns and inflation.Hourly to Salary CalculatorConvert an hourly wage to annual, monthly, biweekly, weekly and daily pay, with overtime.Bonus Tax CalculatorEstimate take-home pay on a bonus: 22% federal supplemental rate, FICA and state tax.Self-Employment Tax CalculatorCalculate Social Security and Medicare self-employment tax (15.3%) and the deductible half.Price per Square Foot CalculatorFind price per sq ft or m², total price or area, and compare several homes by value.Real Estate Commission CalculatorCalculate realtor commission, the agent and broker split, and the seller's net proceeds.Rent Split CalculatorSplit rent fairly between up to 6 roommates by room size, income or equally.Car Affordability CalculatorSee how much car you can afford with the 20/4/10 rule or your monthly budget.Daily Interest CalculatorInterest per day and total interest for any number of days, simple or compounded daily.Contribution Margin CalculatorContribution margin per unit, CM ratio, operating profit and break-even point.Customer Acquisition Cost CalculatorCAC from marketing and sales spend, plus LTV:CAC ratio and payback months.CPA CalculatorCost per acquisition from ad spend, plus break-even and target CPA from your margin.Average Order Value CalculatorAverage order value from revenue and orders, plus the revenue impact of raising AOV.Reorder Point CalculatorReorder point from daily demand, lead time and safety stock, with days until the next order.Safety Stock CalculatorSafety stock by days of cover, max − average, or service level (Z × σ × √lead time).Dimensional Weight CalculatorDIM weight and billable weight for a box in inches or cm with 139, 166, 5000 or 6000 divisors.Food Cost CalculatorPlate cost per portion, food cost percentage and menu price for any recipe.Growth Rate CalculatorTotal growth, compound growth rate per period, linear average and a projection.RPM CalculatorRevenue per 1,000 views from earnings, estimated earnings from RPM, and views for a goal.Customer Retention Rate CalculatorCustomer retention rate and churn from start, end and new customer counts.Margin to Markup CalculatorConvert gross margin % to markup % and back, with price multiplier and conversion table.Army Body Fat CalculatorArmy tape test body fat (2023 one-site or legacy method) vs AR 600-9 standards by age.Steps to Miles CalculatorConvert steps to miles and km from your height or step length, with time and calories.Swimming Pace CalculatorSwim pace per 100 m or yd, speed and splits from distance and time, plus CSS from a test.Blood Pressure CalculatorBlood pressure reading to AHA category, mean arterial pressure and pulse pressure.Waist to Height Ratio CalculatorWaist to height ratio in cm or inches with health bands and the 0.5 rule waist target.Fiber Intake CalculatorDaily fiber target from age, sex and calories (14 g per 1,000 kcal and IOM table).Alcohol Units CalculatorUK alcohol units from volume and ABV, plus a weekly total vs the 14-unit guideline.hCG Doubling Time CalculatorTwo hCG results and hours apart to doubling time and the equivalent 48-hour rise.IVF Due Date CalculatorIVF due date from a day 3, 5 or 6 embryo transfer or egg retrieval, with weeks pregnant.Baby Formula CalculatorEstimate daily and per-feed baby formula in ml and oz from weight, age and feeds.Barbell Plate CalculatorWhich plates to load on each side of the bar for any target weight, in kg or lb.Wilks CalculatorPowerlifting Wilks 2020 and DOTS scores from body weight, sex and total in kg or lb.GFR CalculatorEstimate eGFR from creatinine, age and sex with CKD-EPI 2021 and see the CKD stage.Mean Arterial Pressure CalculatorCalculate mean arterial pressure (MAP) and pulse pressure from a blood pressure reading.Cat Food CalculatorHow much wet and dry food to feed your cat per day, from weight, life stage and activity.Cat Pregnancy CalculatorFind your cat’s due date from the mating date, with a week-by-week pregnancy calendar.Sleep Debt CalculatorFind your weekly sleep debt from hours slept per night and get a simple recovery plan.Screen Time CalculatorSee your daily screen time per year and over your lifetime, and what else you could do.Book Reading Time CalculatorHow long a book takes to read from its pages or words and your reading speed.Pages per Day CalculatorHow many pages to read each day to finish a book by your date, with a reading schedule.Zakat CalculatorCalculate 2.5% zakat on cash, gold, silver and investments against the gold or silver nisab.House Flipping CalculatorFix-and-flip profit, ROI and 70% rule max offer from purchase, rehab, holding and sale costs.Airbnb Income CalculatorShort-term rental net income from nightly rate, occupancy, cleaning, fees and expenses.EV vs Gas Car Cost CalculatorCompare yearly EV charging vs gas fuel costs, cost per mile, savings and CO₂ emissions.Simplify Fractions CalculatorReduce any fraction to lowest terms with GCD steps, mixed number, decimal and equivalents.Cubic Equation SolverSolve ax³ + bx² + cx + d = 0 for real and complex roots with steps and a graph.Vector Calculator2D and 3D vectors: add, subtract, dot and cross product, magnitude, angle, unit vector, projection.Complex Number CalculatorAdd, subtract, multiply, divide complex numbers; polar form, modulus, argument, powers and roots.Summation CalculatorEvaluate sigma notation: sum any expression in n from a to b with partial sums and a chart.Arithmetic Sequence CalculatorFind the n-th term, sum and full list of an arithmetic sequence, or d from two terms.Geometric Sequence CalculatorFind the n-th term, sum and infinite sum of a geometric sequence, or r from two terms.Fibonacci CalculatorExact n-th Fibonacci number (BigInt), sequence lists, Fibonacci check and golden ratio.Pascal's Triangle GeneratorGenerate Pascal's triangle up to row 30, highlight a row and expand (ax + by)ⁿ.Binomial Distribution CalculatorBinomial probabilities P(X = k), at most, at least or between, with mean, variance and chart.Normal Distribution CalculatorNormal probabilities P(X < x), between two values and inverse percentiles, on a shaded bell curve.Poisson Distribution CalculatorPoisson probabilities for a rate λ: exactly k, at most, at least or between, with a chart.T-Test CalculatorOne-sample, two-sample (Welch/pooled) and paired t-tests with p-value and CI.Chi-Square CalculatorChi-square goodness-of-fit and independence tests with p-value and expected counts.P-Value CalculatorOne- or two-tailed p-values from z, t, chi-square or F statistics, with critical values.Variance CalculatorSample and population variance and standard deviation with a step-by-step deviations table.Five Number Summary CalculatorMin, Q1, median, Q3, max, IQR and fences of a data set, with a box plot.Outlier CalculatorFind outliers with 1.5×/3× IQR fences, z-scores or modified z-scores; get the cleaned data.Geometric Mean CalculatorGeometric, harmonic, arithmetic and quadratic means compared, or average growth from % changes.Expected Value CalculatorExpected value, variance and standard deviation from outcomes and their probabilities.Trigonometry CalculatorSin, cos, tan, csc, sec, cot and inverses in degrees or radians, with exact values.Arc Length CalculatorArc length, sector area and chord from radius and angle, or solve for the radius or angle.Cylinder Volume CalculatorCylinder volume in liters, gallons and cubic units from radius or diameter, plus surface area.Regular Polygon CalculatorArea, perimeter, apothem, radius and angles of a regular polygon from any one measurement.Golden Ratio CalculatorSplit a length into golden sections, find a from b, and get a φ scale of design sizes.Factors CalculatorAll factors and factor pairs of a number, prime factors, divisor count and perfect check.Big Number CalculatorExact + − × ÷ mod and powers for huge integers with hundreds of digits, plus digit count.RC Time Constant Calculatorτ = RC, charge % at 1-5τ, and capacitor charge or discharge voltage at any time t.Resonant Frequency CalculatorLC resonant frequency f = 1/(2π√LC), or solve the inductance or capacitance you need.Capacitor Series and Parallel CalculatorTotal capacitance of capacitors in series or parallel, plus stored energy ½CV² and charge.Three-Phase Power CalculatorkW, kVA and kVAR from volts, amps and power factor, or three-phase current from kW or kVA.Generator Size CalculatorAdd appliance running and starting watts to find the generator size you need.Pressure CalculatorSolve P = F/A for pressure, force or area in Pa, kPa, bar, psi and atm.Work CalculatorSolve W = F·d·cos θ for work, force, distance or angle in J, kWh and ft-lb.Hooke's Law CalculatorSolve F = kx for spring force, spring constant or extension, plus stored spring energy.Centripetal Force CalculatorCentripetal force and acceleration from mass, radius and speed or RPM: F = mv²/r.Gravitational Force CalculatorNewton's law of gravitation F = Gm₁m₂/r² for any two masses, with planet presets.Speed of Sound CalculatorSpeed of sound from air temperature or medium, and distance from an echo or thunder delay.Doppler Effect CalculatorObserved frequency from source and observer speeds, or source speed from a pitch shift.Specific Heat CalculatorSolve Q = mcΔT for heat energy, mass, specific heat or temperature change, with materials.Percent Yield CalculatorPercent yield from actual and theoretical yield, or theoretical yield from moles and formulas.PPM CalculatorConvert ppm to mg/L, %, ppb and mg/kg, find ppm of a solution, or ppm to mg/m³ for gases.Grams to Moles CalculatorConvert grams to moles and back from a chemical formula, with molar mass and atom counts.Decibel CalculatorAdd dB levels, convert power or voltage ratios to dB, and find sound level at a distance.Pipe Flow Rate CalculatorFlow rate from pipe diameter and velocity (GPM, L/s, m³/h), velocity from flow, or pipe size.Stud CalculatorCount wall studs and plates from wall length, spacing, corners and openings.Carpet CalculatorCarpet for your rooms in sq ft and sq yd from a 12 or 15 ft roll, with padding and cost.Baseboard CalculatorLinear feet of baseboard and number of pieces for your rooms, minus doorways.Grout CalculatorGrout in kg, lb and bags from tile size, joint width, depth and area.Rebar CalculatorRebar for a slab grid: bars each way, total length, weight by bar size and stock bars.Asphalt CalculatorTons of asphalt from area and thickness at 145 lb/ft³, with volume and cost.Sand CalculatorSand in cubic yards, m³, tons and bags for any area and depth.Retaining Wall CalculatorBlocks, caps, base gravel and drainage stone for a block retaining wall.Siding CalculatorSiding squares, panels and J-channel from walls and gables minus doors and windows.Pool Chlorine CalculatorHow much liquid chlorine, bleach or shock to add to reach a target free chlorine.Aquarium Volume CalculatorFish tank gallons, liters and water weight: rectangle, cylinder, bow-front and hexagon tanks.Fertilizer CalculatorPounds of fertilizer and bags for your lawn from N-P-K and a target rate per 1,000 sq ft.Raised Bed Soil CalculatorSoil for raised garden beds in cubic feet, cubic yards, liters and bags, with mix recipes.Plant Spacing CalculatorHow many plants fit an area at a given spacing, in a square, triangular or row pattern.LED Savings CalculatorYearly savings, kWh saved and payback time when switching old bulbs to LED.Tank Volume CalculatorTotal and filled volume of cylinder, rectangular and capsule tanks in gallons and liters.Rainwater Harvesting CalculatorGallons or liters of rainwater a roof collects from its area, rainfall and surface.Quarter Mile CalculatorEstimate 1/4 mile ET and trap speed from horsepower and weight, or HP from a time slip.Compression Ratio CalculatorStatic engine compression ratio from bore, stroke, chamber, gasket, deck and piston volume.Concrete Steps CalculatorConcrete volume and bags for poured steps from step count, rise, run, width and landing.Weighted Grade CalculatorCurrent class grade from weighted categories, plus the score you need on the final.SGPA to CGPA CalculatorCGPA from semester SGPAs and credits, with percentage by ×9.5, ×10 or VTU formula.GPA to Percentage CalculatorConvert a 4.0, 5.0 or 10-point GPA to a percentage and back with common formulas.Meat per Person CalculatorHow much raw meat to buy for a party or BBQ from guests, meat type and appetite.Rice to Water Ratio CalculatorExact water and cook time for any rice in cups or grams: stovetop, rice cooker or Instant Pot.Yeast ConverterConvert fresh, active dry, instant yeast and sourdough starter by grams, teaspoons or packets.Butter ConverterConvert butter between sticks, cups, tablespoons, grams, ounces and 250 g EU blocks.Cake Servings CalculatorHow many wedding or party slices a round, square or sheet cake serves, tier by tier.Fabric Yardage CalculatorHow many yards or meters of fabric to buy for your pieces, width, seams and pattern repeat.Depth of Field CalculatorNear and far focus limits, depth of field and hyperfocal distance for any camera or lens.Crop Factor CalculatorCrop factor, full-frame equivalent focal length and aperture, and field of view for any sensor.Print Size CalculatorPrint size from pixels and DPI, max print size by megapixels, and pixels needed for any print.3D Printing Cost CalculatorCost and selling price of a 3D print: filament, power, machine wear, failures and labor.