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Good decisions start with clear examples.
Practical explanations with the numbers left in. Read a worked example, open its calculator, and change the assumptions to match your own situation.
HousingWhat a $5,000 mortgage lump sum changes a year into repaymentFollow a dated $300,000 mortgage example with one $5,000 principal payment, a capped final payment and a downloadable monthly schedule.Read the worked example →BusinessHow to calculate blended margin across two product linesCombine product-line revenue and cost correctly, see why averaging margin percentages can mislead, and reconcile the result to markup.Read the worked example →BusinessA lower business-loan rate can hide a larger borrowing costCompare two hypothetical $10,000 business loans: 10% with $1,000 deducted fees versus 12% without fees. Follow usable proceeds and repayments.Read the worked example →Loans and debtTrading in a car with debt: where the negative equity goesTrace a $10,000 trade-in with a $12,000 payoff through a new auto purchase, rebate, sales tax, fees and monthly payments.Read the worked example →BusinessWhen does a $12,000 equipment investment pay back?Include setup and ongoing costs in an equipment purchase. Follow $400 monthly net cash benefits to a 30-month simple payback, with downside scenarios.Read the worked example →Housing15-year vs 30-year mortgage: payment and interest tradeoffsCompare how mortgage term and rate assumptions change the monthly principal-and-interest payment and lifetime interest.Read the worked example →Home buyingWhat an extra $100 a month changes on a mortgageA transparent $300,000 mortgage example: compare payoff time and interest with an extra $100 monthly, then edit the assumptions yourself.Read the worked example →ResaleIs a resale pallet worth buying? Count the unsold itemsWork through a 50-item resale lot with damaged stock, fees and fulfillment costs. See how sell-through changes profit and try the example yourself.Read the worked example →Business & truckingThe empty return trip that changes your cost per mileA worked trucking example separates all miles from paid miles and shows why deadhead changes the break-even rate without changing the truck's total costs.Read the worked example →
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Our decision guides organize existing calculators into mortgage, resale, debt, saving and business workflows. The articles above go deeper into specific questions rather than replacing those guides.
How we prepare these articles
Published September 10, 2026. Examples are hypothetical, with arithmetic checked against our calculator code. Sources explain the underlying concepts; they do not endorse Fair Calcs or establish the example rates as current offers. These articles are educational estimates, not personal financial, tax or professional advice.