Learn the money behind the math
Clear, practical guides to the concepts behind our calculators — how mortgages, debt, and compounding actually work, and how to use the numbers.
Guides
401(k) vs IRA vs Roth: Which Should You Use?How 401(k), traditional IRA, and Roth accounts differ on taxes and access, plus a simple order for using them.Read guide APR vs Interest Rate: What's the Difference?APR vs interest rate explained: what each measures, why APR is usually higher, and how to compare loan offers correctly.Read guide Auto Loans: How to Get the Best DealHow to finance a car smartly: price vs payment, down payment, trade-in, sales tax, term length, and credit score.Read guide Building an Emergency FundWhy you need an emergency fund, how many months to save, where to keep it, and how to build it step by step.Read guide CAC and LTV: The Two Numbers Every Business Should TrackWhat customer acquisition cost and lifetime value mean, how to calculate each, and why the LTV:CAC ratio (around 3:1) signals a healthy business.Read guide Debt Avalanche vs Snowball: Two Ways to Get Out of DebtThe debt avalanche saves the most interest; the snowball builds momentum. How each method works and how to choose the right one.Read guide Dollar-Cost Averaging vs Lump-Sum InvestingLump-sum vs dollar-cost averaging: why lump-sum usually beats DCA on paper, when averaging in still makes sense, and how to choose for a windfall.Read guide Estimated Taxes for Freelancers and the Self-EmployedHow estimated quarterly taxes work for the self-employed: why they exist, the 2025 deadlines, the safe-harbor rule, and how much to set aside.Read guide Evaluating a Rental PropertyHow to analyze a rental: NOI, cap rate, cash-on-cash return, and gross rent multiplier — what each tells you.Read guide Gross vs Net Pay: Where Your Paycheck GoesThe difference between gross and net pay, the deductions in between, and why pre-tax contributions help.Read guide Home Equity Loan vs HELOC: Which One FitsHome equity loan vs HELOC explained: fixed lump sum vs revolving line, fixed vs variable rate, and which one fits your project.Read guide How 401(k) Employer Matching WorksHow 401(k) employer matches are structured, what vesting means, and why you should always contribute enough to get the full match.Read guide How APY Works (and How It Differs from APR)APY explained: the annual percentage yield formula, a worked example, why compounding frequency matters, and how APY differs from APR.Read guide How Capital Gains Tax WorksHow capital gains tax works in the US: the one-year holding rule, long-term rates of 0/15/20%, and how losses offset gains.Read guide How Car Lease Payments Work (Money Factor Explained)Car lease payments explained: depreciation, finance charge and tax, how the money factor converts to APR, and what residual value means.Read guide How Compound Interest Builds WealthCompound interest explained simply: why time beats amount, the Rule of 72, and what drives long-term investment growth.Read guide How Credit Card Balance Transfers WorkBalance transfers explained: how a 0% intro APR works, the 3-5% transfer fee, when it saves money, and how to pay the balance off in time.Read guide How Credit Card Interest Really WorksHow credit card interest is calculated: the daily periodic rate, compounding, the grace period, and why minimum payments cost you.Read guide How Crypto Taxes Work in the USCrypto is taxed as property: which events are taxable, what isn't, short-term vs long-term gains, and why cost-basis records matter.Read guide How Much Do You Need to Retire?How to estimate your retirement number from your spending, the 4% rule, the 25x guideline, and why inflation matters.Read guide How Much House Can You Afford?How to work out your real home budget from income, debts, down payment, and full PITI — the way lenders actually decide.Read guide How PMI Works and How to Avoid ItPMI explained: when private mortgage insurance is required, typical rates, how it is calculated, and how to remove or avoid it.Read guide How Property Taxes Work (Assessed Value & Mill Rate)Property tax explained: how assessed value and the mill rate set your bill, why it differs from market value, and how exemptions and appeals lower it.Read guide How Social Security Benefits Are CalculatedHow Social Security works: your top 35 earning years, AIME, the PIA formula, full retirement age, and how claiming early or late changes your check.Read guide How to Fill Out a W-4 (and Set Your Withholding)A plain-language guide to the W-4: how withholding works, how to complete each step, and when to update it to avoid a surprise tax bill.Read guide How to Finance Home Improvements: Loan vs HELOC vs Cash-OutCompare ways to pay for a renovation: personal home-improvement loan, HELOC, home-equity loan, and cash-out refinance — with the trade-offs of each.Read guide How to Pay Off Credit Card Debt FasterProven ways to clear credit card debt: pay above the minimum, snowball vs avalanche, and balance transfers.Read guide How to Start Investing: A Beginner's RoadmapA simple order of operations for new investors: emergency fund, debt, employer match, then steady, diversified investing.Read guide Renting vs Buying a HomeRenting vs buying: the true costs of ownership, why the five-year rule matters, the break-even point, and the opportunity cost of a down payment.Read guide Required Minimum Distributions (RMDs) ExplainedWhat RMDs are, why they start at age 73, how the required amount is calculated, and the penalty for missing the deadline.Read guide Rule 72(t) / SEPP: Penalty-Free Early Retirement WithdrawalsRule 72(t) explained: how SEPP lets you withdraw from an IRA or 401(k) before 59 1/2 without the 10% penalty, the three IRS methods, and the risks.Read guide Self-Employment Taxes: A Freelancer's GuideHow self-employment tax works, why freelancers pay both halves of FICA, the deductible half, and quarterly payments.Read guide Should You Consolidate Your Debt?When debt consolidation saves money, the main tools (personal loan, balance transfer, home equity), and the trap that leaves people worse off.Read guide Should You Pay Off Your Mortgage Early?When paying off your mortgage early makes sense, how extra and biweekly payments work, and when to invest instead.Read guide The 4% Rule ExplainedWhat the 4% rule is, where it comes from, what it assumes, and why some retirees use a lower rate.Read guide The BRRRR Method ExplainedHow the BRRRR real-estate strategy works step by step, why the 70% rule and ARV matter, and the risks of recycling your down payment.Read guide US Income Tax Brackets ExplainedHow US tax brackets work: marginal rates, why a raise doesn't tax all your income more, and marginal vs effective rate.Read guide Understanding Bonds and YieldsHow bonds work: coupons, why price and yield move opposite, and current yield vs yield to maturity.Read guide Understanding Mortgage PointsHow mortgage discount points work, what one point costs, the break-even calculation, and when buying down your rate is worth it.Read guide Understanding Your Mortgage Payment (PITI)PITI explained: principal, interest, taxes, and insurance. Learn what makes up a monthly mortgage payment and why the rate is only part of it.Read guide What Affects Your Credit ScoreThe five factors behind your credit score, why payment history and utilization dominate, and how to improve fastest.Read guide What Counts as a Good ROI?How to read return on investment properly: the ROI formula, why annualizing matters, sensible benchmarks, and the inflation test.Read guide What Is Credit Utilization (and the 30% Rule)Credit utilization explained: how the balance-to-limit ratio is calculated, why the 30% rule matters for your score, and how to lower it fast.Read guide What Is Debt-to-Equity RatioDebt-to-equity ratio explained: the total-liabilities-over-equity formula, what a healthy D/E looks like, and why it varies by industry.Read guide What Is Debt-to-Income (DTI) and Why It MattersDebt-to-income ratio explained: how DTI is calculated, the 28/36 rule, the thresholds lenders use, and how to lower it.Read guide What Is Loan-to-Value (LTV) and Why It MattersLoan-to-value explained: how LTV is calculated, the 80% threshold that avoids PMI, and how a lower LTV earns better mortgage rates.Read guide What Is an Escrow Account (Mortgage Escrow)Mortgage escrow explained: how lenders collect property tax and insurance monthly, the annual escrow analysis, shortages, and when escrow is required.Read guide When Does Refinancing Your Mortgage Make Sense?How to decide if refinancing is worth it: the break-even test, good reasons to refinance, and the costs involved.Read guide
Glossary
All terms →1031 Exchange40172(t) / SEPPAdjustable-Rate MortgageAmortizationAnnuityAPRAPYBalance TransferBalloon PaymentBondBurn RateCap RateCapital GainsCash AdvanceCash-on-Cash ReturnChurn RateClosing CostsCompound InterestCoupon RateCredit ScoreCredit UtilizationCustomer Acquisition CostCustomer Lifetime ValueDiscount PointsDiversificationDividendDollar-Cost AveragingDown PaymentDTIEffective Tax RateEquityEscrowEstimated TaxesFICAFixed-Rate LoanFUTAGross IncomeGross MarginGross Rent MultiplierInflationInterest RateLiquidityLTVMarginal Tax RateMinimum PaymentNet IncomeNet WorthNOIPITIPMIPresent ValuePrice-to-Rent RatioPrincipalReal ReturnRefinancingResidual ValueReturn on Ad SpendRoth IRASelf-Employment TaxSimple InterestStandard DeductionTax WithholdingTaxable IncomeTraditional IRAUSDA LoanVestingYieldYield to Maturity