Calculate your average accounts payable (beginning ap + ending ap) / 2. Identify your total purchases for the period. Webhow to calculate accounts payable? You can calculate the accounts payable by generating accounts payable aging summary report, if you are using. Webknowing how to calculate accounts payable (ap) can give you a clear picture of what your business owes, helping you avoid cash crunches. Staying on top of. Webaccounts payable turnover ratio is an ap metric that informs you about how quickly your organization makes payments to creditors and suppliers. It's a key measure of back.