BASIS.
Cost basis for options, and what the next buy does to it
01

Average cost

× per contract
—
no fills yet
02

Fills

Price paid, contracts taken
# Price Contracts Cost
Start with the price you paid and how many you took.
03

The next buy

Modelled, not taken
$

Enter a price to model the next buy.

The average bends toward the price and never arrives. The first contract does most of the work, the tenth almost none.
04

Target average

The inverse question
$
$

Name the average you want and the price you can get.