{"id":"acct-mid-month-upgrade-proration","audience":"accounting","category":"finance-work","track":"finance","technique":"verification","level":"intermediate","title":"Prorate a mid-month plan upgrade and compute the extra amount due","free":false,"task":"You're billing a customer who upgraded mid-month. Write a prompt for plain text with lines starting \"Old plan days:\", \"New plan days:\", \"November charge:\", \"Already billed:\" and \"Additional due:\", each with the math. Prorate by days in a 30-day November. The new plan starts on Nov 16. Don't mention the free month the rep joked about. Under 80 words. No bullets or numbering.","materialLabel":"Plan change details (attached to your prompt automatically)","material":"PLAN CHANGE - Harbor Lane Bakery, November 2026\n\nOld plan: $100.00 per month. New plan: $160.00 per month.\nThe customer upgraded on Nov 12 and the new plan starts on Nov 16, 2026.\nNovember has 30 days. Billing is monthly in advance; the November invoice for $100.00 was issued Nov 1 and paid.\nMethod: charge each plan for the days it applies, using the monthly price x days / 30. Days on the old plan are Nov 1 to Nov 15; days on the new plan are Nov 16 to Nov 30.\n\nNotes: the sales rep told the customer 'maybe we can throw in a free month someday'; nothing was agreed or approved. The next full invoice, Dec 1, will be $160.00.","rules":[{"type":"plainText"},{"type":"maxWords","max":80},{"type":"maxBullets","max":0}],"promptHints":[{"label":"Names the five lines","patterns":["old plan days","new plan days","november charge","already billed","additional due"]},{"label":"Gives the date ranges","patterns":["nov 1","nov 16"]},{"label":"Gives the formula","patterns":["x .* days / 30","/ 30"]},{"label":"Bans the free month","patterns":["(do not|don'?t).*free"]},{"label":"Caps length","patterns":["\\d+\\s*words","plain"]}],"mistakes":[{"title":"Charging the full new price","why":"The AI bills $160 for November and shows $60 additional.","fix":"Say: \"Charge each plan for the days it applies: price x days / 30.\"","checks":["r1","r2"]},{"title":"Mentioning the free month","why":"The AI adds the rep's free month comment.","fix":"Add: \"Do not mention any free month.\"","checks":["r2"]},{"title":"Wrong day counts","why":"The AI counts the upgrade date Nov 12 as the start.","fix":"Add: \"The new plan starts Nov 16: 15 days on each plan.\"","checks":["r0"]},{"title":"Markdown extras","why":"The AI adds bold labels, headings and a closing note.","fix":"Say: \"Plain text, no bold. Output only the lines asked for.\"","checks":["plainText","maxBullets"]},{"title":"Trusting the AI to count words","why":"AI is bad at counting and runs past word limits.","fix":"Ask for fewer words than the real cap and keep each line short.","checks":["maxWords"]}],"hint":"Proration depends on the start date of the new plan and a 30-day month. Give the days, the formula and the ban.","rubricLabels":["The line starting \"Old plan days:\" shows 15 (Nov 1 to Nov 15) and the line starting \"New plan days:\" shows 15 (Nov 16 to Nov 30)","The line starting \"November charge:\" shows $100.00 x 15 / 30 + $160.00 x 15 / 30 = $50.00 + $80.00 = $130.00","The line starting \"Already billed:\" shows $100.00 and the line starting \"Additional due:\" shows $130.00 - $100.00 = $30.00, with no mention of a free month"]}