Forecast from calculated field

Is it possible to provide a forecast based on a calculated field?

The use case is that I have a daily item count and I’d like to forecast the cumulative daily count over time. I currently create a running total and it is this value I would like to forecast.

Alternatively I thought of forecasting the item count but then I don’t think I can use forecast data in a running sum for the running total.

Could you push down the calculation into SQL?