The payment date indicates the date of your credit card issuer actually charges the bill from your account while the settlement date indicates the date when the division between payable balance and outstanding balance occurs.
A typical credit card issuer allows users to decide the payment dates by themselves.
Having said that, if the settlement date is the 15th of each calendar month, the payable balance would be expensed between the 15th from the previous calendar month to the 14th of the current calendar month. Any other expenses that occur after those dates, would be considered an outstanding balance.
For example, if you set up the settlement date as the 15th of each calendar months and
today is 19th Mar,
Payable Balance: 15th of Feb – 14th of Mar
Outstanding Balance: 15th of Mar – 14th of Apr
And then, on the 15th of May,
Payable Balance: 15th of Mar – 14th of Apr
Outstanding Balance: 15th of Apr – 14th of May
However, please ensure that if there is an outstanding balance prior to the settlement of payable balance or additional charges occur, these amounts will be included in the payable balance. Therefore, the settlement date indicates the beginning of your calendar month in terms of payable balance.