The method. Not a mystery.

RB Math is a short, editorial purchase check. It organizes what you tell us; it does not verify your finances or decide what you should value. There are three verdicts, no score and no claim of scientific validation.

Five core answers. Three screens.

We ask the full price, whether the money is ready, whether the item earns a place in your life, whether you would choose it without pressure, and whether there is a genuine alternative. An item name and estimated wears are optional. A cheaper alternative needs its own price and a separate confirmation.

What each answer means

Money ready: you have set aside the full cost without new borrowing, carrying a purchase balance or taking from essentials, existing debt commitments, emergency needs or other priorities you choose. A credit card paid in full is not the same as carrying a balance. This is your assessment, not a professional affordability check.

Earns a place: fit and practical use are confirmed; the item fills a need or has meaning to you. Special occasions can count. There is no universal cost-per-wear threshold.

Without pressure: you would choose it without the sale, countdown or social pressure. Uncertainty calls for a pause, not a diagnosis.

The exact decision order

1. Use what you own: when you explicitly select an already-owned option that does the job and you would use, the verdict is DUPE IT. No new spending is required, so this can apply even if the new item is unfunded.
2. Check real use and clarity: without confirmed use or a choice independent of pressure, the verdict is SKIP & STACK. This can mean “not yet,” without adding a fourth verdict.
3. Check a lower-priced alternative: DUPE IT requires a strictly lower price and explicit confirmation that you would choose it, it meets your fit and quality needs, and its full cost has its own funding. The alternative can clear even when the more expensive original cannot.
4. Check the original: WORTH IT requires confirmed funding, use and clarity, with no confirmed alternative you would choose instead. Otherwise the verdict is SKIP & STACK.

A cheaper option you have not confirmed does not automatically block a funded original. The tool does not search retailers or verify quality. “DUPE IT” means a legitimate alternative, never a counterfeit or an assertion of identical craftsmanship.

The useful arithmetic

Optional cost per wear = full price ÷ estimated wears. Wears are assumptions, not a durability promise. Price difference = original price − alternative price. Using something you own avoids a new purchase but does not create money.

No phantom savings: a result never automatically sends the price or difference to Future You. You enter the amount you actually have available. Nothing on this site moves money or confirms that money was saved.

Future You: contributions first

The starting example is $0 now plus $25 at the end of each month for one year, with no growth assumption: $0 + $25 × 12 = $300 contributed. It is an illustration, not a suggested personal savings amount. You can change all those inputs.

The optional compounding view initially uses an explicitly hypothetical 5% nominal annual change, compounded monthly—not a current rate, forecast or recommended investment return. Negative and zero scenarios are allowed. Choosing a purpose does not change the calculation or recommend where to hold money.

i = annual percentage ÷ 100 ÷ 12; n = years × 12
FV = P(1+i)ⁿ + M[(1+i)ⁿ−1] ÷ i
At zero: FV = P + M × n
Contributions = P + M × n; change = FV − contributions.

P is the amount now; M is the month-end deposit. Fixed rates do not model volatility. Taxes, fees, inflation, changing contributions and withdrawals are excluded. Negative rates model only one simplified loss scenario. The allowed input range is not a forecast range. A nominal annual rate compounded monthly differs from an effective annual return.

Separate classroom example: the lesson with $100 at 5% compounds annually: $100 × 1.05 = $105; $105 × 1.05 = $110.25. It deliberately uses a different, clearly stated frequency for teaching.

A deliberately new experience

Version 4 replaces the previous weighted, 100-point questionnaire with these simpler disclosed rules. Missing answers are never filled in to manufacture a score. The full details remain here for anyone who wants them.