{
  "id": 18738520,
  "title": "My calculators gave correct answers to the wrong questions, so I started asking back",
  "url": "https://urgent.news/2026/11/07/my-calculators-gave-correct-answers-to-the-wrong-questions-so-i",
  "topic": "tech",
  "section": "Tech",
  "published": "2026-11-07T15:45:01.000Z",
  "source": {
    "name": "Dev.to",
    "slug": "dev-to",
    "url": "https://dev.to/vintage97/my-calculators-gave-correct-answers-to-the-wrong-questions-so-i-started-asking-back-4ge3"
  },
  "original_language": "en",
  "account": "When I tested my calculators by simulating real user input, I discovered that the issues weren't related to incorrect math calculations. The problem lay in the input itself—people often typed different numbers than they meant. My tools needed a change to address this issue. You can access the updated compound interest calculator at https://instantfreetools.com/compound-interest-calculator/.\n\nInterest rates can appear in two ways—percentages like 5% or decimal form like 0.05. My compound interest field expects percentages, so 0.05 actually means 0.05%. The discrepancy between the two can be significant. For instance, $10,000 invested for 10 years at 5% compounded monthly results in $16,470.09, while at 0.05%, it becomes $10,050.12. Both results are mathematically correct based on the input, but only one aligns with what the person intended. Simply multiplying numbers below 1 by 100 to convert them isn't an ideal solution. A 0.5% savings rate, for example, shouldn't be automatically turned into 50%.\n\nInstead, the page keeps the input as typed and asks, \"Using 0.05%. Did you mean 5%?\" with a button to switch to the correct value. If the rate is above 0 and below 1, the page asks whether the user meant a larger percentage. For rates already above 1, no question appears. I added rounding to avoid displaying numbers like 7.000000000000001% instead of 7%.\n\nAnother example is the BMI calculator, which has a height field labeled in centimeters (cm). When I typed 1.75, which many people write as their height, it calculated a BMI of 228,571.4— clearly incorrect. I made a silent change to correct this by reading any value between 0 and 3 in the cm box as meters. The result then explicitly states, \"Read 1.75 as 175 cm.\" This conversion is not hidden and helps prevent misunderstandings.",
  "summary": "When I tested my calculators the way people actually type, the first problems I found were not about wrong maths. The maths was right. The input was a different number from the one the person meant, and the page answered that number with full confidence. I made these tools, and this is what I changed so they ask back instead: https://instantfreetools.com/compound-interest-calculator/ A 5% rate…",
  "key_points": [
    "Calculators misinterpreted user input, giving wrong answers",
    "Updated compound interest calculator addresses percentage vs decimal input issue",
    "BMI calculator now correctly interprets height input in centimeters"
  ],
  "editors_take": null,
  "illustration": null,
  "coverage": {
    "outlets": 1,
    "also_reported_by": []
  },
  "ai_generated": true,
  "disclaimer": "Summaries, key points and the editor’s take are written by software from other outlets’ reporting and may contain errors — always check the linked original."
}