Sales Forecasting Google Sheet

I need a custom-built Google Sheet that lets me drop in historical sales figures and instantly see reliable forecasts for the months ahead. The core of the file should centre on accurate sales forecasting, so you may lean on built-in functions like FORECAST, LINEST, or even a lightweight Apps Script if that gives us cleaner automation.

Here is what I’m looking for:

• A clean data-entry tab where I can paste raw daily or monthly sales numbers.
• A forecasting engine that updates automatically when new rows are added, displaying projected totals, growth rates, and confidence intervals.
• Visual outputs—at minimum a time-series chart and a summary dashboard—so trends are obvious at a glance.
• Clearly commented formulas or script sections, allowing me to tweak assumptions later without breaking the model.

Acceptance criteria: When I enter at least 12 months of sales data, the sheet must refresh without manual re-runs, show next-period projections, and recalc in under five seconds. Share permissions should remain with me as owner when delivered.

If you’ve tackled similar Google Sheets, let me know how you handled the forecasting logic and any optimisation tricks you used to keep large datasets responsive.