{"id":"sheet-re-mortgage-pmt-formula-explained","audience":"real-estate","category":"spreadsheets","track":"data","technique":"audience","title":"Get a mortgage payment formula you can explain to buyers","free":false,"task":"You want a buyer-facing sheet where C2 shows the monthly principal-and-interest payment as a positive number, from the loan amount in A2, the yearly rate in B2 and a 30-year term. Ask for one formula for C2 in one code block, then exactly 2 numbered lines labeled Means: (plain words for a first-time buyer, no function names) and Check: (the payment for $400,000 at 6%). Under 50 words outside the code.","materialLabel":"Your payment sheet (attached to your prompt automatically)","material":"Sheet: Payment estimator (Excel), shared with buyers\n\nA Loan amount | B Yearly rate | C Monthly payment (P&I)\n400,000 | 6.0% |\n350,000 | 6.5% |\n520,000 | 5.875% |\n\nNotes:\n- B is formatted as a percent (6.0% is stored as 0.06)\n- All loans in this sheet are 30-year fixed\n- Taxes and insurance are on another tab, not in C\n- My first try, =PMT(B2,30,A2), showed -24,000-something and buyers panicked\n- First-time buyers read this at open houses on a tablet","rules":[{"type":"codeBlocks","count":1},{"type":"numberedItems","count":2},{"type":"maxProseWords","max":50}],"mistakes":[{"title":"Leaving the term vague","why":"The AI uses the yearly rate and 30 periods, the same mistake as your first try.","fix":"Add: \"Monthly payment: rate / 12, 360 months.\"","checks":["r0"]},{"title":"Not asking for a positive number","why":"Excel shows loan payments as negative, which scares buyers.","fix":"Add: \"Show it as a positive number.\"","checks":["r1"]},{"title":"Explaining to the wrong reader","why":"The AI explains PMT arguments, which means nothing to a buyer.","fix":"Add: \"Means: plain words for a first-time buyer, no function names.\"","checks":["r2","numberedItems"]},{"title":"Getting a menu of options","why":"The AI likes to offer two or three versions of the formula, so you're left to pick and test them yourself.","fix":"Add: \"Give one formula only, in one code block, no alternatives.\"","checks":["codeBlocks"]},{"title":"Getting a tutorial","why":"By default the AI explains every part of the formula at length.","fix":"Add: \"Each line under 20 words. Nothing else.\"","checks":["maxProseWords"]}],"promptHints":[{"label":"Asks for a monthly payment","patterns":["/\\s*12","monthly","360"]},{"label":"Asks for a positive number","patterns":["positive","not negative","minus"]},{"label":"Says who reads it","patterns":["buyer","first-time","plain"]},{"label":"Asks for a check","patterns":["check","400,?000"]},{"label":"Asks for one formula","patterns":["one formula","one code block","single formula","no alternatives"]}],"hint":"Payment formulas trip on monthly vs. yearly and on the minus sign. Spell out both, and say who will read the explanation.","rubricLabels":["The formula divides the yearly rate by 12 and uses 360 months (30*12), for example =-PMT(B2/12,30*12,A2)","The formula returns a positive number (a minus sign before PMT, or a negative loan amount)","After the code there are 2 numbered lines labeled Means: (plain words, no function names) and Check: ($400,000 at 6% is about $2,398 a month)"]}