20 guides · 51 glossary terms

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

MortgageUnderstanding Your Mortgage Payment (PITI)What actually makes up a monthly mortgage payment — principal, interest, taxes, and insurance — and why the sticker rate is only part of the story.Read guide BudgetWhat Is Debt-to-Income (DTI) and Why It MattersYour debt-to-income ratio is the single number lenders lean on most. Here's how it's calculated, what counts, and the thresholds that decide your rate.Read guide InvestmentHow Compound Interest Builds WealthCompound interest is the engine behind long-term investing. Here's why time matters more than amount, and how to estimate your own growth.Read guide MortgageHow Much House Can You Afford?Income, debts, down payment, and the full PITI payment all decide your real budget. Here's how lenders — and you — should do the math.Read guide MortgageShould You Pay Off Your Mortgage Early?Extra payments can save tens of thousands in interest — but they aren't always the best use of your money. The trade-offs, laid out.Read guide MortgageWhen Does Refinancing Your Mortgage Make Sense?Refinancing can lower your rate or payment — but closing costs mean it only pays off if you stay long enough. Find your break-even.Read guide LoansAPR vs Interest Rate: What's the Difference?They sound the same but they aren't. Knowing the difference is how you actually compare loan offers apples-to-apples.Read guide LoansAuto Loans: How to Get the Best DealPrice, down payment, trade-in, term, and sales tax all move your real cost. Here's what actually matters when financing a car.Read guide Credit CardsHow to Pay Off Credit Card Debt FasterHigh APRs make credit card debt brutal. The payoff strategies that actually work — and the math behind them.Read guide Credit CardsWhat Affects Your Credit ScoreFive factors decide your score, and two of them dominate. Knowing them is how you improve it fastest.Read guide InvestmentHow to Start Investing: A Beginner's RoadmapYou don't need a lot of money or expertise to begin. The order of operations that sets beginners up to win.Read guide InvestmentUnderstanding Bonds and YieldsBonds trade on price and yield, which move opposite each other. The core concepts every investor should know.Read guide Retirement401(k) vs IRA vs Roth: Which Should You Use?The main US retirement accounts differ mostly in taxes and access. A simple framework for choosing.Read guide RetirementHow Much Do You Need to Retire?Your number depends on your spending, not someone else's. How to estimate it — and why inflation matters.Read guide RetirementThe 4% Rule ExplainedThe most cited rule of thumb in early retirement — where it comes from, what it assumes, and its limits.Read guide TaxesUS Income Tax Brackets ExplainedA raise never pushes your whole income into a higher tax rate. How marginal brackets actually work.Read guide TaxesSelf-Employment Taxes: A Freelancer's GuideWorking for yourself means paying both halves of Social Security and Medicare. What to set aside and why.Read guide SalaryGross vs Net Pay: Where Your Paycheck GoesThe number on your offer letter isn't what lands in your account. A tour of the deductions between gross and net.Read guide Real EstateEvaluating a Rental PropertyCap rate, cash-on-cash, NOI, and GRM each answer a different question. The metrics that separate a deal from a dud.Read guide BudgetBuilding an Emergency FundThe foundation of every financial plan. How much to save, where to keep it, and how to get there.Read guide

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