Yes, there is a function in Excel that can help you calculate the finance charge on a credit card. The function you can use is called the "PMT" function.

Here's how you can use the PMT function to calculate the finance charge:

1. First, you need to know your credit card's annual percentage rate (APR). Let's say your APR is 18%.
2. Next, you need to know your credit card's average daily balance (ADB). To calculate your ADB, add up your daily balances for the billing cycle and divide by the number of days in the billing cycle. Let's say your ADB is $1,000.
3. Now, you can use the PMT function to calculate the finance charge. The formula for the PMT function is:
   Formula:

   =PMT(rate/365, days, balance) 

   . In this formula, "rate" is your APR, "days" is the number of days in the billing cycle, and "balance" is your ADB. So, for example, if your billing cycle is 30 days, the formula would be:
   Formula:

   =PMT(0.18/365, 30, 1000) 

   . This will give you the finance charge for that billing cycle.
4. If your payment date is not the same every month, you can adjust the formula by changing the "days" parameter to reflect the number of days between your payment date and the end of the billing cycle. For example, if your payment date is 10 days before the end of the billing cycle, you would use "20" instead of "30" for the "days" parameter.