Forecasting with Cost Explorer
A forecast is a prediction of how much you will use AWS over the next three months, based on your past usage. Forecasting provides an estimate of what your AWS bill will be, and enables you to use alarms and budgets for amounts that you are predicted to use. Because forecasts are predictions, the forecasted billing amounts are estimated, and might differ from your actual charges for each statement period.
Like weather forecasts, billing forecasts can vary in accuracy. Different ranges of accuracy have different confidence intervals. The higher the confidence interval, the more likely the forecast is to be correct. For example, say you have a budget set to 100 dollars, and you've used 75 dollars in the past three weeks. Cost Explorer forecasts that there is an 80% probability that your billed costs will be in the 90 to 100 dollar range, and an 95% probability that your billed costs will be in to 80 to 110 dollar range.
Cost Explorer forecasts have confidence intervals of 95% and 80%. If AWS does not have enough data to forecast within an 95% confidence interval, Cost Explorer does not show a forecast.
How you read the Cost Explorer forecasts depends on the type of chart that you're using. Forecasts are available for plot and bar charts, but not for stacked bar charts.
When you use plot charts, there are two sets of lines on either side of your costs line. The pair of lines that are closest to the cost line indicate the 80% confidence interval, and the pair of lines that are furthest from the cost line indicate the 95% confidence interval. The wider the range included in the forecast, the higher the probability that your bill will fall in the forecasted range.
When you are using bar charts, there are two sets of lines on either side of the top of your bar. The closer, darker lines indicate the 80% confidence interval, and the further, fainter lines indicate the 95% confidence interval. The wider the range included in the forecast, the higher the probability that your bill will fall in the forecasted range.
Using Forecasts with Consolidated Billing
If you are using consolidated billing, the paying account's forecasts will be calculated with the data from all of the accounts in the consolidated billing family. After you add a new linked account to the family, forecasts are less accurate until the new spending patterns of the consolidated billing family are analyzed.