Total payback
Multiply the advance by the factor rate. This is the total you will repay, whatever the term.
Cost of funds
Subtract the advance from the total payback. This is what the money costs, in dollars.
Net deposit
Subtract any origination fee from the advance. This is what actually reaches your account. Judge the cost against the net deposit, since you repay on the full advance.
The payment
Divide the total payback by the number of business days in the term for a daily payment, or by the number of weeks for a weekly one.
Share of your sales
Divide the payment by what your account receives on a slow day. If it takes a large share, the advance may be too heavy. Count any advances you already pay as well.