For the predicted next order date, we simply add the average time between the appropriate order counts to the last order date of the customer in question. For example, if a customer has placed 2 orders, we'll take the average time from your ecommerce report between the 2nd and 3rd order for all customers, and add this time to their last order date to get the predicted date for their next order.
The predicted spend is calculated in exactly the same fashion; we take the spend from the customer's last order and add it to the average difference in order spend based on the order count of what will be their next order.
It's worth remembering that the predicted order date and value are generated using fairly basic mathematics. The larger your order file the more accurate these are likely to be, but there's not some hugely complex machine learning algorithmic process involved. We just include these columns as a little indicator to aid with customer targeting.