Finding the maximum bid for achiving a specific discount over retail
2026-02-01:
With the variables defined, now we can work backwards and then solve for the bid.
Last but not least, while solving for B, I tried a number of AI assistants. The winner ended up being ChatGPT, which was able to isolate B on the left side of the equation.
So this weekend, I set about solving a problem that was bothering me. When purchasing a pewpew at auction, what should the maximum bid be, assuming we want a specified percentage discount off the retail new price for a given item?
Building on an existing formula I had worked out to calculate the savings percent over retail, I started working backwards.
Assumptions
- Auction items will require shipping
- Auction items will include tax plus an auction fee
- Auction items may or may not have shipping insurance
- Auction items will have a credit card payment fee
- Retail price will not include shipping
- Average Sale price info available online won’t include shipping, insurance, or credit card fees.
Variables
With the variables defined, now we can work backwards and then solve for the bid.
Last but not least, while solving for B, I tried a number of AI assistants. The winner ended up being ChatGPT, which was able to isolate B on the left side of the equation.