45 guides • Formula in plain words • Reviewed September 2026

Calculator Guides & How-To Articles

Each guide is the judgement layer for a calculator: the formula in words, a worked example, and the next tool in the job. Use the matching calculator when you want the number.

Finance & money guides

23 guides

Mortgages, debt, student loans and saving. Each guide explains the formula in words, works an example and points to the matching calculator.

Rent at 30 percent of a 60,000 dollar salary is about 1,500 dollars a month
Renting5 min read
How Much Rent Can I Afford? 30% Rule by SalarySpend no more than about 30% of gross income on rent: $1,500 a month on a $60,000 salary. See rent by salary, the 40x landlord rule and hidden costs.Read the guideSpending 72,000 dollars a year needs about 1,800,000 dollars at a 4 percent withdrawal rate
Retirement6 min read
How Much Do I Need to Retire? The 25x Rule ExplainedSave 25 times your annual spending: $72,000 a year needs about $1,800,000 at a 4% withdrawal rate. See the table, where the rule comes from and its limits.Read the guideA 75,000 dollar salary supports roughly a $272,000 home under the 28/36 rule with 20 percent down
Home buying6 min read
How Much House Can I Afford on a $75,000 Salary?The 28/36 rule suggests about $272,000 on a $75,000 salary with 20% down and no other debts. See the table by salary and a worked example.Read the guideSaving 500 dollars a month reaches 10,000 dollars in 20 months
Savings goals5 min read
How Long Does It Take to Save $10,000? Monthly Plan ChartSaving $500 a month reaches $10,000 in 20 months. See how long it takes at other monthly deposits, and the deposit needed for any deadline.Read the guideA 20 percent down payment on a 400,000 dollar house is 80,000 dollars
Down payment6 min read
How Much Down Payment Do You Need for a $400,000 House?20% down on a $400,000 house is $80,000; 3% is $12,000. See the loan, PMI and monthly payment at 3%, 5%, 10% and 20% down.Read the guideAn emergency fund of three to six months of essential expenses is the common guideline
Emergency fund5 min read
How Many Months of Expenses Should an Emergency Fund Cover?Most guidance suggests 3-6 months of essential expenses: $10,500-$21,000 on $3,500 a month. See targets by situation and a worked example.Read the guideRefinancing 300,000 dollars from 7 to 6 percent with 6,000 dollars of closing costs breaks even in about 30 months
Refinancing6 min read
How Long Does It Take to Break Even on a Refinance?Divide closing costs by monthly savings: $6,000 of costs and $197 saved a month breaks even in about 30 months. Table by closing costs and rate drop.Read the guideA 5,000 dollar credit card balance is paid off in 34 months at 200 dollars a month and 22 percent APR
Credit card payoff6 min read
How Long to Pay Off $5,000 Credit Card Debt? Payment Chart$5,000 at 22% APR takes 34 months at $200 a month and costs about $1,750 in interest. See payoff times for $100 to $500 payments.Read the guideA 4.50 percent CD earns $450 in interest on 10,000 dollars in 12 months
Savings6 min read
CD vs High-Yield Savings Account: Which Earns More?A locked 4.50% CD earns $450.00 on $10,000 in a year; a savings account earns more only if its rate stays at or above the CD's. See the comparison and break-even rule.Read the guideA 300,000 dollar loan at 6.5 percent over 30 years has a monthly payment of about 1,896 dollars
Formula breakdown5 min read
Monthly Mortgage Formula Explained SimplyLearn the monthly mortgage formula M = P[r(1+r)^n]/[(1+r)^n-1]. Worked $300,000 example, Excel PMT, taxes, PMI, and amortization.Read the guideA 240,000 dollar loan at 6.5 percent over 30 years has a payment of about 1,517 dollars a month
Amortization6 min read
How to Calculate a Mortgage Payment Step by StepLearn how to calculate a mortgage payment step by step: the formula, a worked $240,000 example, an amortization schedule, and how rate, term and down payment change...Read the guideA 240,000 dollar loan at 6.5 percent over 30 years is about 1,517 dollars a month
Mortgages6 min read
Mortgage Calculator Guide: Estimate Payments, Interest & AffordabilityLearn how to use a mortgage calculator to estimate monthly payments, total interest, loan affordability, down payments, taxes, insurance, and the effect of extra...Read the guideThe VA funding fee is 2.15 percent for first-time use with no down payment
Mortgages11 min read
VA Home Loan Calculator Guide: Funding Fee, Taxes & Monthly PaymentLearn how to calculate a VA home loan payment, including the VA funding fee, taxes, and insurance. See sample payments by home price and how down payment changes the fee.Read the guideThe avalanche method saves 178 dollars in interest compared with the snowball method on 14,700 dollars of debt
Debt strategy3 min read
Debt Avalanche vs. Snowball: Real Numbers on $14,700 in DebtAvalanche vs snowball with an actual worked example: three real debts, exact months, exact interest saved. Plus the 0% balance transfer breakeven math.Read the guidePaying 300 dollars a month extra pays off a 400,000 dollar mortgage 7.8 years early
Mortgages & investing5 min read
Extra Mortgage Payments vs. Investing: The Real Math (2026)Should you pay extra on your mortgage or invest the difference? Worked numbers on a $400,000 loan, biweekly payment savings, PMI removal timing, and points breakeven...Read the guideA 6,000 dollar debt paid at 250 dollars a month looks like 24 months before interest
Debt strategy8 min read
Debt Payoff Calculator Guide: How Payment Changes Your Debt-Free DateLearn how payment size, interest rate, and balance change your debt-free date. Use the CalculatePilot Debt Payoff Calculator to compare realistic payoff strategies...Read the guideA debt-to-income ratio of 36 to 43 percent is a caution zone; above 43 percent is high risk
Debt2 min read
What Is a Good Debt-to-Income Ratio?A good DTI ratio is below 36%. Learn what debt-to-income ratio means, how to calculate front-end and back-end DTI, and what lenders actually look for.Read the guideA 30,000 dollar student loan at 6.5 percent over 10 years is about 340 dollars a month
Student loans2 min read
How to Calculate Student Loan Payments (2026 Guide)Student loan payment formula explained. A $30,000 loan at 6.5% over 10 years = $340/month. Full breakdown by loan amount, rate, and term with payment tables.Read the guideFour steps for SAVE plan borrowers to take before the deadline
US policy 20264 min read
SAVE Plan Borrowers Face a Deadline This Month — What It Means for Your PaymentA SAVE repayment plan deadline this month could raise monthly payments for federal student loan borrowers who don't switch plans in time. Here's what's happening and...Read the guideFour steps to check whether refinancing a car loan saves money
Car loans8 min read
Car Loan Refinance Calculator Guide: Check If Refinancing Saves MoneyLearn how to use a car loan refinance calculator: gather your payoff balance and rate, compare a new offer, and read monthly savings versus total interest before you...Read the guideAn emergency fund for six months of 3,200 dollars of essential expenses is 19,200 dollars
Saving7 min read
Emergency Fund Calculator Guide: Build a Cash Reserve That Fits Your Real LifeUse an emergency fund calculator to set a practical savings target based on essential expenses, income stability, dependents, and unexpected costs.Read the guideFour stages of 529 college savings by child age
Education planning5 min read
529 Calculator by Age: How Much Should You Save for College?Use a 529 calculator by age to estimate college savings growth, monthly contributions, future college costs, and funding gaps. Includes examples for different ages.Read the guideA 529 plan growing to about $84,975 after 15 years with 250 dollars a month at 6 percent
Education planning2 min read
529 College Savings Calculator: Growth, Contributions & ExamplesLearn how a 529 college savings calculator estimates future value, monthly contributions, growth and college funding targets with practical examples.Read the guide10,000 dollars at 5 percent compounded monthly grows to about 16,470 dollars in 10 years
Investing2 min read
How to Calculate Compound InterestCompound interest formula explained: A = P(1 + r/n)^(nt). Learn how to calculate compound interest with worked examples for savings, investments, and loans.Read the guideA 100 dollar item at 25 percent off costs 75 dollars
Everyday money2 min read
Discount Calculator Guide: Calculate Sale Price & SavingsLearn how to calculate discounts, sale prices, and savings with simple percentage formulas and examples. Includes discount plus tax and reverse discount examples.Read the guide

Math & conversion guides

10 guides

Open these when a calculator gives you a number you still need to interpret, such as scientific notation, a triangle solution, a slope or a time zone.

Percentage change equals new minus old divided by old times 100
Percentages5 min read
Percentage Calculator: Percent, IncreaseLearn how to calculate percentages, percentage increase and decrease, and find what percent one number is of another with worked examples.Read the guideThree formulas cover most percentage calculations
Math baseline2 min read
How to Calculate Percentages — Complete Guide with ExamplesHow to calculate percentages: find X% of a number, percentage increase/decrease, and what percentage one number is of another. Formula and worked examples.Read the guide12,345,678 written in words
Text and numbers2 min read
Number to Words Converter: How to Spell Numbers in WordsLearn how to convert numbers to words for checks, forms, invoices, and documents. See examples, rules, and common mistakes with a free number to words converter.Read the guideScientific notation writes a number as a times 10 to the power n
Powers of ten2 min read
Scientific Notation Calculator GuideLearn how to convert decimals to scientific notation and back. Understand coefficients, positive and negative exponents, formulas, and worked examples.Read the guideA triangle with sides 5, 6 and 7 has angles of about 44.4, 57.1 and 78.5 degrees
Geometry3 min read
How to Find Angles of a Triangle from Side LengthsHow to find the angles of a triangle from side lengths using the Law of Cosines. Includes base angles, area formulas, triangle inequality, and a worked 5-6-7 example.Read the guideSlope equals rise divided by run
Coordinate plane2 min read
Slope Calculator Guide: Formula & Slope Between Two PointsLearn how to calculate slope between two points using the slope formula. Covers positive, negative, zero, and undefined slopes with examples.Read the guideVolume of a box equals length times width times height
Solids2 min read
Volume Calculator Guide: Formulas for Common ShapesLearn volume formulas for cubes, rectangular boxes, cylinders, spheres, cones, and other shapes with simple worked examples.Read the guidearccos of negative one equals 180 degrees or pi radians
Trigonometry2 min read
Cos Inverse -1 = 180°Find cos inverse of -1 instantly: arccos(-1) = 180° = π radians. Learn why, see the unit-circle explanation, degree/radian forms, and use the trigonometry calculator.Read the guideFive feet ten inches equals 177.8 centimeters
Conversion2 min read
Height Calculator Guide: Feet, Inches & CM ConversionLearn how to convert height between feet, inches, centimeters, and meters with simple formulas, examples, and a height conversion table.Read the guideLocal time equals UTC time plus the UTC offset
Time zones2 min read
UTC Time Converter Guide: Convert UTC to Local TimeLearn how UTC works, how to convert UTC to local time, calculate UTC offsets, and understand the difference between UTC and GMT.Read the guide

Health & everyday guides

11 guides

BMI is a screening tool, not a diagnosis. The car and moving-cost guides explain how the estimate is worked out.

A due date is 280 days after the first day of the last menstrual period
Pregnancy5 min read
How to Calculate Your Due Date: LMP, Conception & IVFAdd 280 days to the first day of your last period: 1 March 2026 gives 6 December 2026. Adjust for cycle length, or use conception (+266 days) or IVF dating.Read the guideAn 82 kilogram moderately active adult needs about 98 to 131 grams of protein a day
Nutrition5 min read
How Much Protein Do I Need Per Day? Chart by WeightMultiply weight in kg by 0.8-2.2 depending on activity: an 82 kg moderately active adult needs about 98-131 g a day. Chart by weight and activity.Read the guideHome size and distance are the main drivers of moving cost
Budgeting a move5 min read
Moving Cost Calculator: Estimate Your Moving CostsLearn how to estimate moving costs by home size, distance, labor, packing, storage and other expenses with a practical moving cost calculator guide.Read the guideA 32,000 dollar car keeps about 44.4 percent of its value after five years
Car depreciation6 min read
Car Depreciation Chart: Value by Year & How to Calculate ItUnderstand car depreciation by year with a clear value-retention chart, depreciation formula, worked example, and factors such as mileage, condition.Read the guideA 500 calorie daily deficit leads to about 1 pound of weight loss per week
Weight loss6 min read
How Many Calories to Eat to Lose 1 Pound a Week?Eat about 500 calories below your maintenance level to lose roughly 1 pound a week. See daily targets by TDEE and weekly rate, with a worked example.Read the guideAbout 2,410 steps burn 100 calories at 160 pounds and a moderate walking pace
Walking & calories5 min read
How Many Steps Burn 100 Calories? Chart by Weight & PaceAbout 2,410 steps burn 100 calories for a 160 lb adult at a moderate pace. See the chart by body weight and walking speed, plus the formula.Read the guideRecommended pregnancy weight gain is 25 to 35 pounds in total for a normal pre-pregnancy BMI with one baby
Pregnancy6 min read
How Much Weight Should I Gain in Pregnancy? Chart by WeekRecommended pregnancy weight gain by pre-pregnancy BMI: 25-35 lb total for normal weight, about 7-12 lb by week 20. IOM chart by week and BMI category.Read the guideA score of 92 percent is needed on a final worth 30 percent to finish with an 85 percent course grade
Grades5 min read
What Grade Do I Need on My Final Exam? Formula & ExamplesFind the score you need on your final to reach your target grade. Formula, tables and worked examples, e.g. 82% going into a 30% final needs 92% for an 85%.Read the guideA normal adult BMI is between 18.5 and 24.9
Body composition2 min read
What Is a Good BMI? BMI Ranges ExplainedA healthy BMI is 18.5 to 24.9. Learn what BMI means, how it is calculated, what the different ranges indicate, and its limitations as a health measure.Read the guideBMI equals weight in kilograms divided by height in meters squared
Screening5 min read
BMI Calculator Guide: What Your Number Really MeansA practical guide to BMI — what it measures, how to calculate it, who it misleads, and which other health metrics to track alongside it.Read the guideA new car loses 20 to 30 percent of its value in the first year
Vehicle ownership2 min read
Car Depreciation Chart 2026 — How Much Value Does a Car Lose Per Year?Car depreciation chart 2026: new cars lose 20-30% in year one, 15-20% per year after. Full breakdown by year, make, and model type. Free depreciation calculator.Read the guideA local two-bedroom move costs about 600 to 1,500 dollars
Budgeting a move2 min read
How Much Does It Cost to Hire Movers? (2026 Guide)Moving costs in 2026: local moves average $800–$2,500, long-distance $2,000–$7,500+. Full breakdown by home size, distance, and service type.Read the guide
Fast track

Open the calculator, not another article

Guides do not replace the tool. If you already know the job, go straight to the calculator that produces the number.

Mortgage calculatorUK mortgage repaymentUK stamp dutyUK student loan repaymentUK take-home payScotland take-home payDebt payoff calculatorPercentage calculatorAdult BMI calculatorExplore all calculators
How the guides are written

Author & method

SH
Suhaib HassanAuthor & calculator developer

Writes and maintains the guides alongside the calculators they explain, and checks each worked example against the tool.

Our methodologyFormula-first, example-checked

Guides state their assumptions. Figures such as tax rates and thresholds change, so check the date on each guide and the official source before acting.

Comparisons

1 guide

Side-by-side comparisons of CalculatePilot with other calculator sites and tools: what each does best, with sources you can check.

CalculatePilot vs Calculator.net: two free calculator sites compared side by side
Comparison6 min read
CalculatePilot vs Calculator.netHow this library differs on formulas, privacy and embeds.Read the comparison