How EV is computed

Every CS2 weapon case has a fixed pool of skins sorted into five rarity tiers. Valve publishes the per-tier drop probability — those numbers, multiplied by live skin prices, give the expected value of one unboxed item.

1. Valve drop odds

2. Per-skin expected price

For each skin s with available wears W:

price_normal(s)    = mean over w in W of bestPrice(s, w)
price_stattrak(s)  = bestPrice("StatTrak™ " + s) if listed, else 1.4 × normal
price_expected(s)  = 0.9 × price_normal(s) + 0.1 × price_stattrak(s)

bestPrice is the lowest live ask across Steam Market, CSFloat, and Skinport.

3. Case EV

EV_tier(t)  = mean over s in tier_t of price_expected(s)
EV_gross    = Σ over tiers t of P(t) × EV_tier(t)
EV_net      = EV_gross − caseUnitPrice − keyUnitPrice
EV_pct      = EV_net / (caseUnitPrice + keyUnitPrice)

Two ways we show ROI

The same expected value can be quoted two ways, and we show both:

• Unboxing ROI = EV / cost — the share of your spend you get back on average. A Kilowatt at $1.33 EV on $2.81 cost is 47%: you keep about 47¢ of every dollar.
• Net ROI = (EV − cost) / cost — your gain or loss. Same case = −53%.

They're the same number shifted by 100% (net = unboxing − 100%). Unboxing ROI is the headline figure on cards; net is shown alongside. Anything under 100% unboxing ROI (i.e. negative net) loses money — which is almost every container.

5. Lottery score

Most cases have a deeply negative mean dominated by rare knife / glove drops. A high σ/μ means the case is essentially a lottery ticket: most opens lose almost everything and a few wins carry the EV. A low score means a more consistent — though usually still negative — outcome.

Caveats

• Wear distribution is approximated as uniform across listed wears. Real Valve distribution is float-uniform within each skin's allowed float range.
• Steam Market's 15% seller fee is not deducted. Third-party markets (CSFloat, Skinport) charge much less, and our bestPrice already prefers the lowest live ask.
• When all three sources fail for a skin, it's treated as $0 and the case is flagged as "lower-bound EV".
• This is not financial advice. Don't open cases as an investment.

Data sources

• Case + skin metadata: ByMykel/CSGO-API (committed snapshot, refreshed via npm run fetch-metadata)
• Steam Market: steamcommunity.com/market/priceoverview
• CSFloat: public listings API
• Skinport: api.skinport.com/v1/items

Prices are cached server-side for 30 minutes. Click "Refresh prices" on any page to invalidate and re-pull.