Take the number of chargebacks over a particular period of time, divide it by the total number of transactions, and multiply by 100 in order to present it as a percentage. Different card brands have slightly different methods for calculating chargeback ratios. For example, Visa calculates chargeback rates by dividing a particular month’s chargebacks by that particular month’s total number of transactions while MasterCard divides a particular month’s chargebacks by the previous month’s total transactions.