How to Forecast Sales in Google Sheets with ChatGPT
Predicting future sales often feels like guesswork, but you can build a surprisingly accurate forecast right inside Google Sheets with a little help from ChatGPT. This approach combines the flexibility of a spreadsheet with the analytical power of AI, without needing a degree in statistics. This tutorial will walk you through preparing your data, using ChatGPT to generate forecasting formulas, and visualizing the results for clear, actionable insights.
First, Get Your Sales Data in Order
A reliable forecast starts with clean, historical data. Before you can predict the future, you need a clear picture of the past. The more high-quality historical data you have, the more accurate your forecast will be. Ideally, you should have at least 12-24 months of data to identify meaningful trends and seasonal patterns.
Open a new Google Sheet and structure your data with clear, simple columns. At a minimum, you'll need two columns:
Date: The period of the sale (e.g., daily, weekly, or monthly). Use a consistent format like MM/DD/YYYY. Monthly data is often the best starting point for high-level business forecasting.
Revenue: The total sales revenue for that period.
For a more detailed forecast, you can include additional columns that might influence sales numbers, such as:
Units Sold: The number of products sold.
Marketing Spend: How much was spent on advertising during that period.
Unique Website Visitors: Traffic data can be a leading indicator of sales.
Product Category: To forecast sales for specific product lines.
Before moving on, quickly scan your data for any errors or inconsistencies. Ensure there are no gaps in the dates and that all revenue figures are formatted as numbers. A tidy dataset is the foundation of a good forecast.
Understanding Common Sales Forecasting Methods
There are many ways to forecast sales, from simple averages to complex statistical models. You don't need to be an expert in all of them, but knowing the basics helps you ask ChatGPT for the right kind of analysis. Here are a couple of popular methods that work well in Google Sheets.
Moving Averages
A moving average smooths out short-term fluctuations in your data to give you a clearer view of the underlying trend. To calculate it, you average the sales data from a specific number of recent periods — for example, a 3-month moving average uses the average of the last three months' sales. It's a great method for businesses with relatively stable sales that don't have strong seasonal patterns.
Linear Regression
If your sales have been constantly growing or declining over time, linear regression is a better choice. This method essentially draws the "best-fit" straight line through your data points and extends that line into the future to predict sales. Google Sheets has a built-in function, FORECAST.LINEAR, that makes this calculation straightforward, and ChatGPT can help you write the formula perfectly.
Using ChatGPT as Your Data Analysis Assistant
This is where the process becomes much faster. Instead of searching for tutorials on how to write specific spreadsheet formulas, you can simply ask ChatGPT. The key is to provide a small sample of your data and a clear, specific prompt.
A quick note on privacy: Never paste sensitive customer or financial data into ChatGPT. Use anonymized sample data from your sheet. A dozen rows are usually enough for ChatGPT to understand the structure.
Example 1: Forecasting with a Moving Average
Let's say you want to create a 3-month moving average to predict next month's sales. Your data starts in row 2, with dates in Column A and revenue in Column B.
Copy about 10 rows of your data from Google Sheets.
Go to ChatGPT and write a prompt like this:
Prompt: "I have sales data in a Google Sheets file. Column A contains the month, and Column B contains the revenue. I want to calculate a 3-month moving average in a new Column C to forecast sales for the following month. My data starts on row 2. What formula should I enter in cell C4 and then drag down?"
ChatGPT will likely give you this formula:
Now, go back to your Google Sheet, click on cell C4, paste the formula, and press Enter. Click the small blue square in the corner of the cell and drag it down to the last row of your data. This column now shows you your moving average forecast, where each cell predicts the next month's sales based on the average of the previous three.
Example 2: Forecasting with Linear Regression
If your sales show a steady trend, a linear forecast is more appropriate. You can ask ChatGPT to help with this, too.
Prompt: "Using the same Google Sheets data (Column A for dates, Column B for revenue from B2:B25), I want to forecast sales for the next month, which corresponds to the date in cell A26. Can you give me the formula using the FORECAST.LINEAR function?"
ChatGPT should provide a formula like this:
This formula tells Google Sheets to:
Look at the future date in A26.
Analyze the known revenue data in the range B2:B25.
Correlate it with the known dates in the range A2:A25.
Predict a value based on the established trend.
You can create a new column named "Linear Forecast" and paste this formula at the end of your data to predict values for future periods. Just add the upcoming dates in Column A, and copy the formula down to get your forecast for the next several months.
Asking ChatGPT for Deeper Analysis
ChatGPT can do more than just write formulas. It can also act as a brainstorming partner to help you interpret your data.
Prompt: "Here is a sample of my monthly sales data for the last year. Based on these numbers, can you identify any potential trends, seasonality, or anomalies I should be aware of? What would be the best way to visualize this data in Google Sheets?"
ChatGPT might point out things you overlooked, such as a consistent sales dip in the summer months or a significant spike every November. This context helps you create a more nuanced forecast by identifying patterns that a simple formula might miss.
Bring Your Forecast to Life with Charts
Numbers in a spreadsheet are useful, but a chart tells a story. Visualizing your actual sales against your forecasted sales makes it easy to see how your business is performing and how accurate your predictions are. Creating a chart in Google Sheets is simple.
Highlight the columns containing your dates, actual revenue, and forecasted revenue.
Navigate to the menu and click Insert > Chart.
Google Sheets will usually default to a line chart, which is perfect for this type of data. If it doesn't, you can select "Line chart" from the Chart editor on the right side of the screen.
Use the Customize tab in the Chart editor to add a title (e.g., "Actual vs. Forecasted Sales"), label your axes, and change colors for clarity.
Your finished chart will give you an immediate visual reference to track your progress and adjust your strategies accordingly.
Tips for a More Accurate Forecast
A sales forecast is a proactive tool, not a static report. Keep these tips in mind to improve its accuracy over time:
Keep Your Data Fresh: Update your spreadsheet with new sales data every month. The more current your data, the more relevant your forecast.
Account for External Factors: Your forecast model won't know about an upcoming marketing campaign, a new product launch, or a competitor's big sale. You may need to manually adjust your forecast to account for these business activities.
Review and Refine: Compare your forecasted sales to your actual sales each month. If there's a big difference, try to figure out why. Was a marketing campaign more successful than expected? Did a holiday slow down sales? Use these insights to refine your next forecast.
Don't Be Afraid to Experiment: Try different forecasting methods. Maybe a 6-month moving average is more accurate for your business than a 3-month one. Use ChatGPT to explore other functions like
GROWTHorTRENDfor different types of predictions.
Final Thoughts
Building a sales forecast in Google Sheets doesn't require a complex BI tool or deep statistical knowledge. By pairing clean historical data with ChatGPT's ability to interpret requests and generate formulas, you can create a powerful, data-driven forecast to guide your business strategy. This process empowers you to move from simply reacting to past performance to proactively planning for the future.
While this spreadsheet method is a fantastic starting point, gathering and cleaning data from different sales and marketing platforms can eat up valuable time. We designed Graphed to streamline this entire process. Instead of downloading CSVs, you just connect your data sources - like Shopify, Google Analytics, or Salesforce - and ask questions in simple English, like "Forecast our sales for the next quarter based on last year's trend." Graphed instantly builds you a live, interactive dashboard, turning hours of work into a 30-second task.