Definition
A trade-up contract is the in-game CS2 function that destroys ten weapon skins of one rarity and creates a single weapon skin of the rarity directly above. The mechanic has existed since 2014 and is the only deterministic way (other than direct purchase) to generate a specific skin from inputs you control.
The five rules
- Ten inputs, all of the same rarity tier.
- Output is exactly one tier above the inputs — never two tiers up, never the same tier.
- Either all ten inputs are StatTrak, or none are. Mixing rejects the contract. The output inherits the StatTrak flag.
- Souvenir skins are not eligible as inputs or outputs.
- Eligible rarities for input: Consumer, Industrial, Mil-Spec, Restricted, Classified. Covert and Contraband cannot be inputs. Knives, gloves, agents, stickers, charms, and music kits are not on the rarity ladder and not in the system.
The collection weight
The output skin is drawn from a collection pool weighted by how many inputs came from each collection. Ten inputs from one collection = 100% chance the output is from that collection. Mixed inputs split the chance proportionally — 7 from Cache + 3 from Mirage = 70% / 30% on output collection.
Once the output collection is picked, the contract draws one output-rarity skin uniformly at random from that collection's output-rarity pool.
The float averaging formula
Output float is fully deterministic:
output_float = (average of 10 input floats) × (skin_max − skin_min) + skin_min
Where skin_max and skin_min are the output skin's float clip boundaries. Float clipping is per-skin — an AWP Asiimov clipped 0.18–1.00 cannot produce a Factory New output regardless of input average, because the formula bottoms out at 0.18 when the input average is 0.
The full derivation, the clipping traps, and five worked examples are in the float averaging formula spoke.
Knives and gloves — the two-step path
A trade-up cannot output a knife or glove directly. The only path is two contracts, run on legacy collections where the Covert tier shares the collection with knife rare-special drops: Classified → Covert step one, then ten Coverts → one knife in step two. Modern case collections (Kilowatt, Gallery, Fever) do not support the two-step.
Why the EV is usually negative
Output prices are quoted gross of the 15% Steam Market fee on the sell side. After fees, a recipe that looks +5% EV on paper is often −10% net. Profitable recipes exist (mostly Industrial-to-Mil-Spec and Mil-Spec-to-Restricted, where input prices are low and one strong output skin dominates the pool) but the bar is positive EV after fees, not gross. The full EV walkthrough lives in the pillar guide.
How the calculator handles trade-up outputs
The inventory calculator prices each item in your Steam inventory regardless of how it was generated — case drop, trade-up output, marketplace buy, Souvenir package — at the current Steam Market median for that exact (skin, exterior, StatTrak) tuple. The float on a trade-up output is read from the inspect-link metadata and shown for collector items where it matters.