Guides
In-depth explainers for the questions behind our tools: how the formulas work, worked examples you can check, and the mistakes worth avoiding.
Finance
Browse finance calculators →How to Calculate a Finance Charge
The three ways card issuers compute interest, a side-by-side example, and how the finance charge on a loan is disclosed.
How to Calculate a Loan Amount
Work out how much you can borrow three different ways, and why the smallest of the three answers is the one that counts.
How to Calculate Compound Interest (Formula and Excel)
Learn the compound interest formula, see how compounding frequency and monthly deposits change the result, and do it all in Excel.
How to Calculate GAP Insurance
Find your own gap between what you owe and what the car is worth, see what GAP covers, and decide whether you need it.
How to Calculate Interest on a Car Loan
See exactly how much interest a car loan charges each day, each month and in total, and how the rate and term change it.
How to Calculate Line of Credit Interest
Daily interest, variable rates, interest-only payments and the jump at repayment, explained with a worked HELOC example.
How to Calculate Money Factor on a Car Lease
The money factor explained in plain English, with the conversion to APR, the rent charge formula and a dealer markup example.
How to Calculate Self-Employed Income for a Mortgage
Lenders don't use your gross sales. Here is how they turn your tax returns into qualifying income, with a worked example of the loan it supports.
How to Calculate Simple Interest
The simple interest formula and its rearrangements, day-count rules, and how simple interest applies to car loans, short-term loans and savings.
How to Calculate Tax Depreciation (MACRS)
MACRS explained in plain English, with the IRS percentages for equipment and the mid-month rule for rental buildings.
How to Calculate Your Middle Credit Score (Mortgage)
Why mortgage lenders use your middle score, how to work it out for one or two borrowers, and what a higher score is worth in dollars.
How to Calculate Your Mortgage Payment
Work out your monthly mortgage payment by hand or in Excel, then add tax, insurance and PMI to see what you'll really pay each month.
How to Find Future Value on a Financial Calculator
Future value step by step, from the formula to the exact keystrokes on the most common financial calculators and the Excel FV function.
How to Calculate an Average (Weighted) Interest Rate
Why a simple average of rates gives the wrong answer, how to weight each rate by its balance, and how to use the result to plan payoff or consolidation.
How to Calculate an Implicit Interest Rate
When a deal shows prices and payments but no rate, the rate is still there. Here is how to uncover it, with lease accounting and consumer examples.
How to Calculate an Interest Rate (Formula and Excel)
Three ways to find an interest rate, depending on what you know, plus how to do each one in Excel and what "equilibrium interest rate" means.
How to Calculate APR (Including Mortgage APR)
What goes into an APR, how lenders calculate it step by step, and how to check a Loan Estimate or credit card rate yourself.
How to Calculate the Student Loan Interest Deduction
The student loan interest deduction step by step, including the phase-out formula, Form 1098-E and a worked example of the tax it saves.
How to Calculate Your Car Loan Payoff Amount
The payoff amount formula, how per diem interest is calculated on an auto loan, and how to read a lender's payoff quote.
How to Find Present Value on a Financial Calculator
Present value step by step, for a single future amount, a stream of payments and a bond, on paper, on a financial calculator and in Excel.
How to Pay Off a Car Loan Early (and Faster)
Six proven ways to finish a car loan sooner, how much each saves on a real loan, and the checks to make before you send extra money.
How to Use a Financial Calculator (TVM Keys Explained)
A plain-English walkthrough of N, I/Y, PV, PMT and FV, with step-by-step keystrokes for the most common financial calculators.
How Loan Interest Works
A plain-English tour of how lenders charge interest, how your monthly payment is calculated, and the levers that make borrowing cheaper.
Saving and Investing Explained
A practical walk through planning with money that grows, from short-term savings goals to retirement, in today's dollars and real returns.