How the math works
This calculator uses the heuristics most professional nonprofit auctioneers and event planners follow:
- Starting bid: 30-40% of fair value. Low enough to be inviting, high enough that you're not giving the item away. Hot items can start lower — they'll bid up. Cold items start higher to push the floor up before they stall.
- Reserve: 50-60% of fair value. The minimum acceptable. Below this you don't release the item — you re-donate or send back to the donor.
- Buy-now: 110-140% of fair value. The "I want it now, stop the bidding" price. Hot items command the higher premium because someone will pay it. Large crowds push buy-now higher (more competition raises the perceived value).
- Bid increment: 5% of fair value. The minimum step a new bid must exceed. Small enough that bidders feel they're making progress, large enough to drive real revenue per cycle.