Updated October 17, 2026 · 10 guides · RSS
Personal finance guides that show the math
These personal finance guides explain the ideas behind the calculators in plain English: how interest builds, why APR and APY differ, how a loan is paid down, how to compare payoff strategies, and how CDs and emergency funds work. Each guide uses computed examples you can check by hand, cites primary sources, and links to the calculators that put the ideas to work.
How Much Should Your Emergency Fund Be? Sizing, Storing, Building
How much emergency fund do you need? Size it from essential expenses, keep it insured and easy to reach, and build it step by step with a realistic plan.
- Size an emergency fund from essential monthly expenses, not income; in this guide's example, $3,110 a month makes six months $18,660.
- Three months is a common floor and six months a common target, with more for irregular income, a single earner or dependents.
- Keep the fund in an insured account you can reach within a day or two, where it earns some interest without market risk.
Which guide should I read first?
Start with How Interest Works if the terms feel unfamiliar, since it explains simple and compound interest and compounding frequency. Then read the guide that matches your situation: borrowing, paying off debt or saving. Each one links to the calculators that fit, so you can move from the idea to your own numbers.
How CDs Work: APY, Terms, Penalties, Ladders and Insurance
How CDs work: fixed terms and APY, what an early-withdrawal penalty really costs, how a CD ladder adds access, and how deposit insurance applies.
Debt payoffBalance Transfer vs. Debt Consolidation Loan: Which Fits Your Debt?
Balance transfer vs. consolidation loan: compare fees, promo expiry, payoff speed and credit impact, with a worked example on $10,000 of card debt.
Debt payoffDebt Avalanche vs. Snowball: A Full Worked Comparison
Debt avalanche vs snowball compared with a full four-debt example: payoff order, months to debt-free, total interest, and when each method makes sense.
BorrowingHow Amortization Works: Schedules, Interest and Extra Payments
How amortization works on a fixed-rate loan: why early payments are mostly interest, how to read a schedule, and what extra payments actually save you.
BorrowingLeasing vs. Buying a Car: Money Factor, Residual and Total Cost
Leasing vs. buying a car explained: how money factor, residual value and mileage limits work, with a worked three-year and six-year cost comparison.
Interest basicsAPR vs. APY vs. Interest Rate: What Each Number Tells You
APR vs APY explained: what each number measures, why loans quote APR and savings quote APY, and how Truth in Lending and Truth in Savings rules apply.
BorrowingHow Car Loans Work: Term, Interest, Down Payment and Trade-Ins
How car loans work, from term length and total interest to down payments, negative equity and pre-approval versus dealer-arranged financing.
Debt payoffCredit Card Interest Explained: Daily Rates, Grace Periods, Minimums
How credit card interest works: the daily periodic rate, average daily balance, the grace period, and why paying only the minimum stretches debt for years.
Interest basicsHow Interest Works: Simple vs. Compound Interest Explained
How interest works on loans, cards and savings: simple vs. compound interest, daily accrual, and why compounding frequency changes what you pay or earn.
Frequently asked questions
How long does it take to read a guide?
Most guides take ten to fifteen minutes to read in full, but each one opens with a short answer and key takeaways, so you can get the main point in under a minute. The worked examples are worth the extra time if you plan to act on the numbers.
Are the guides written by financial professionals?
They are written and checked by the CalculateInterestPay Editorial Team against primary sources, with every number verified by computation. We are recruiting credentialed reviewers and will name them on the guides they review once they are in place. Until then, each guide is credited to the team.
Do the guides recommend specific banks or lenders?
No. The guides explain how products work and what usually costs less, but they do not recommend particular banks, lenders or cards. Any future partner links will be clearly labelled and kept separate from guide content. That keeps the explanations useful no matter which institution you use.
How do the guides connect to the calculators?
Each guide links to the calculators that match its topic. Read the guide to understand the idea, then open the calculator to run it with your own numbers. Many calculator pages link back to the guide that explains them in depth.
Will more guides be added?
Yes. New guides are listed in the changelog and, if you subscribe, mentioned in the occasional newsletter. Reader questions sent through our contact page help us decide which topics to cover next. Each new guide follows the same sourcing and computation rules as the existing ones.
Can I print or save a guide?
Yes. Use your browser's print command to print a guide or save it as a PDF. The page layout is designed to print cleanly, with the sources list included. Printed copies show the date, so you can later check whether the guide has been updated since you saved it.
Why do the guides use made-up interest rates?
Rates change often, so quoting today's rates as facts would quickly go out of date. The guides use clearly illustrative rates to show how the math works. For published rate data, see the Federal Reserve and FDIC sources on our resources page.
Can I suggest a correction to a guide?
Yes. Email the corrections address on our contact page with the guide link and what you believe is wrong. We reply within 2 business days, and confirmed errors are fixed within 5 business days with a note on the guide for substantive changes.
Read less, calculate more.
Every guide links to the calculators it explains. Jump straight in.