Injection Molding Cost — Molds, Cycles & Break-Even (2026)
Injection molding is the cheapest way to make a part — after it becomes the most expensive way. The whole game is the mold, the cycle and the volume between them.
Quick answer: Per-piece = resin (pennies) + machine (cycle ÷ 3600 × press rate ÷ cavities) + mold amortization (mold ÷ life shots). A 25 g PP part, 30 s cycle, 4 cavities, $45/h press, $15k mold at 100k shots: $0.28/piece. Molds run $3–15k simple, $20–80k complex; IM beats CNC above roughly 500–5,000 pieces depending on part cost.
The mold is the mountain
- Simple single-cavity prototype tool: $3k–8k
- Production multi-cavity steel tool: $15k–50k
- Complex parts (slides, lifters, textures): $50k–80k+
- Aluminum prototype molds cut the number 40–60% and last 5k–20k shots — the bridge-tool strategy.
Cycle time is wall thickness squared
Cooling dominates the cycle (60–80%), and cooling time scales roughly with the square of the thickest wall. A 2 mm wall part might run 20–30 seconds; doubling to 4 mm can triple the cycle and the machine line of your per-piece cost. Design ribs and coring before you fall in love with chunky walls — every extra second pays rent on every part forever.
Cavities split everything
A 4-cavity mold makes 4 parts per 30-second cycle: the machine line divides by 4 while the mold costs maybe 2–2.5× a single-cavity tool. The calculator shows both layouts' per-piece numbers — the crossover usually lands somewhere around 10k+ annual demand.
The break-even against other processes
At $33 CNC vs $0.28 molded, a $15k mold breaks even near 500 pieces — but that ignores risk (design changes kill molds). Practical wisdom: prototype in 3D printing or CNC, commit to molds when the design is frozen and demand is proven, and quote tooling as a separate line so both sides see the real trade.