Can AI help me decide whether to buy something?

Yes. It works out cost per use, asks the one honest question that matters, and gives you a buy, wait or skip call without judging you.

Verdict: Bot · AI does it well✓ Tested 2 times in Llama 3.3 70B · Oct 27, 2026Written for ChatGPT, Claude or Gemini

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Bot

01Why bot

  • Cost-per-use math is quick and eye-opening.
  • A neutral second opinion helps with impulse buys.
  • It suggests cheaper ways to get the same benefit.
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02The prompt

Replace everything in [BRACKETS] with your own details, then paste it into your AI app.

prompt.txt
You are a calm, practical money coach.

What I want to buy: [ITEM, PRICE]
Why I want it: [REASON]
What I already own that does something similar: [ITEMS]
How often I'd use it: [TIMES PER MONTH]
My monthly fun budget: [AMOUNT]

Your task: help me decide.

Rules:
- MUST work out cost per use over one year and show the math.
- MUST ask me one honest question about whether I'd still want it in a month.
- NEVER shame me for wanting it.

Give me: cost per use, a buy / wait 7 days / skip verdict, and one cheaper way to get the same benefit.

03Steps

  1. Be honest about how often you'd use it.
  2. Run the prompt.
  3. If it says wait, put a reminder in 7 days.

04What can go wrong

  • It's your money and your call.
  • Include accessories and subscriptions in the price.

05What to use

Any major AI chat app.

06Our test runs

2 runs, each with a different made-up sample. 1 of 2 passed every check.

Run 1 · Llama 3.3 70B · graded by GPT-OSS 120BOct 5, 2026Passed

The made-up sample:

  • [ITEM, PRICE]Wireless noise‑cancelling headphones, $199
  • [REASON]I work from home and want to block out background noise during video calls and music listening.
  • [ITEMS]Old wired earbuds, basic over‑ear speakers, and a cheap Bluetooth speaker.
  • [TIMES PER MONTH]12
  • [AMOUNT]$300
  • Calculate cost per use over one year with math
  • Ask one honest question about wanting it in a month
  • Never shame the user
  • Provide cost per use, verdict, and cheaper alternative
  • Didn't make up details we never gave it

What came back (excerpt):

Let's break down the cost per use for the wireless noise-cancelling headphones.
Read the full answer
Let's break down the cost per use for the wireless noise-cancelling headphones. 

You mentioned you'd use them 12 times a month. Since there are 12 months in a year, the total number of uses in a year would be:
12 uses/month * 12 months = 144 uses/year

The cost of the headphones is $199. To calculate the cost per use, we'll divide the cost by the total number of uses in a year:
$199 ÷ 144 uses/year = approximately $1.38 per use

Now, considering your monthly fun budget is $300, this purchase would take up about 66% of your budget for the month.

Here's my honest question: If you had to wait a month before buying these headphones, would you still feel like they're something you really need and want?

Based on our discussion, my verdict is: Wait 7 days. This will give you some time to think about your priorities and whether these headphones are something you truly need right now.

If you're looking for a cheaper way to get the same benefit, you could consider using a noise-cancelling app on your computer or phone, which can help reduce background noise during video calls. Some popular options are free or low-cost, and might be a more budget-friendly solution for you.

Check that the answer includes the required cost‑per‑use calculation and the single month‑delay question.

Run 2 · Llama 3.3 70B · graded by GPT-OSS 120BOct 27, 2026Passed with a catch

The made-up sample (a messier one):

  • [ITEM, PRICE]espresso machine – think a decent mid‑range model, around $480 (maybe $450 if I catch a sale)
  • [REASON]I miss the coffee‑shop vibe at home and want real espresso shots, not the weak stuff my pod machine makes, plus I want to impress guests when they visit.
  • [ITEMS]I already have a cheap pod coffee maker, a French press, and a manual burr grinder that I use for drip coffee.
  • [TIMES PER MONTH]Probably about 10‑12 times a month, maybe a bit more on weekends when I have friends over.
  • [AMOUNT]My fun budget is roughly $150 per month for non‑essentials.
  • MUST work out cost per use over one year and show the math
  • MUST ask me one honest question about whether I'd still want it in a month
  • NEVER shame me for wanting it
  • Give me: cost per use, a buy / wait 7 days / skip verdict, and one cheaper way to get the same benefit
  • Made up details we never gave it

Details it made up: “Number of uses per year: 132 (let's take the average of 120-144 uses)”, “this purchase would take up about 3-4 months' worth of your fun budget.”

What came back (excerpt):

Let's crunch some numbers to help you decide.
Read the full answer
Let's crunch some numbers to help you decide.

You're considering a mid-range espresso machine for around $480 (or $450 if you catch a sale). You plan to use it about 10-12 times a month, which translates to around 120-144 uses per year (assuming you use it the same amount every month).

To calculate the cost per use over one year, let's do the math:

Cost of the espresso machine: $480 (we'll use this as the base price)
Number of uses per year: 132 (let's take the average of 120-144 uses)
Cost per use: $480 ÷ 132 uses = approximately $3.64 per use

Now, considering your monthly fun budget is $150, this purchase would take up about 3-4 months' worth of your fun budget.

Here's my verdict: **Wait 7 days**. This will give you some time to think about your priorities and whether this purchase aligns with your goals.

I have to ask: If you didn't buy this espresso machine today, would you still be thinking about it and wanting it in a month?

As for a cheaper way to get the same benefit, you could consider visiting a local coffee shop or café that offers espresso shots and a cozy atmosphere. This way, you can still enjoy the coffee-shop vibe and impress your guests without the upfront cost of the machine. You could allocate a portion of your fun budget to cover the cost of espresso shots at a coffee shop, which would likely be around $3-5 per shot.

Watch for derived numbers that weren't explicitly given.

How each run works: we fill the prompt with a made-up sample, run it once in Llama 3.3 70B, and GPT-OSS 120B grades the answer against the prompt's own rules. Word limits are counted by code, and every quote flagged as made up is checked against the full answer. Your results can differ. How we test.

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