Invoice amount calculation method, invoice amount calculation device, and printer invoicing system

A manufacturer server 110 that calculates an invoice amount for an inkjet printer has a billing status acquisition unit 342 that acquires billing status information including actual print volume PV, which is the amount of ink used for actual printing not including maintenance, during a specific period L1; an actual print volume calculation unit 343 that determines if actual print volume PV is less than or equal to a specific volume V1; and an invoice amount calculation unit 344 that calculates an invoice amount based on actual print volume PV. When actual print volume PV is the specific volume V1 or less, the invoice amount calculation unit 344 calculates a first invoice amount, which is a fixed amount, as the invoice amount, and when actual print volume PV exceeds the specific volume V1, calculates a second invoice amount that increases with the actual print volume PV as the invoice amount.