Invoice payment terms should be kept to the minimum possible, generally no more than 30 days. The days sales uncollected formula is an equation you can use to estimate the time it takes for a company to receive cash for all its sales.In accounts receivable days, the average AR is calculated as a proportion of (divided by) the total net sales for the business. Then, you take out your gross sales from your accounts receivable to report it to the next month's accounts receivable. The faster a business can collect from customers, the sooner cash is available to fund operations. The formula requires two steps in the calculation. To measure Best DSO, you simply replace "accounts receivable balance" with "current receivables" in the calculation.