In Excel: use =FORECAST.LINEAR(x, known_ys, known_xs) — it predicts a single value from a straight-line fit through your historical points.
On this page8
Syntax
Arguments
| Argument | required / optional | Description |
|---|---|---|
x | required | The point to predict a value for. |
known_ys | required | The observed outcomes. |
known_xs | required | The observed inputs, the same size as known_ys. |
Related functions
Select the result cell and type =FORECAST.LINEAR(.
Enter the x value you want a prediction for, then a comma.
Select the known y values, a comma, then the known x values.
Press Enter. Chart the actuals with the prediction to sanity-check the line.
Need it as an auditable file?
Ships inside the linked template — formula-driven, unlocked, audit-ready.
What this does
FORECAST.LINEAR predicts one y for one x by fitting a least-squares line through the known points. It is identical to computing INTERCEPT plus SLOPE times x, just in one call. The newer FORECAST.ETS handles seasonal time series with exponential smoothing and needs a proper date column; the plain linear form assumes a straight-line relationship and nothing more. The legacy FORECAST still works and matches FORECAST.LINEAR. As with any regression, predictions far outside the observed range of x are extrapolation rather than forecasting. The same idea underpins a lot of everyday Excel work, so the few minutes spent getting it right here pay back across every sheet you build afterwards. Treat it as a pattern, not a one-off, and it stops being something you look up and starts being something you reach for. Treat “forecast formula excel” as a small repeatable workflow rather than a one-off click you hope to remember next time. Use a small test block before the live file, so any surprise in the affected formula shows up while it is still harmless. When a formula is involved, keep the inputs labelled beside it, reference cells instead of typing values, and apply number formatting only after the result checks out. That turns a calculation you can defend to a CFO or an auditor into a method you can reuse, explain, and defend when the workbook leaves your screen.
A worked example
Months 1 to 24 in A2:A25 and revenue in B2:B25: =FORECAST.LINEAR(25, B2:B25, A2:A25) predicts month 25. For a seasonal series with real dates, =FORECAST.ETS(newDate, B2:B25, A2:A25) captures the repeating pattern a straight line cannot. FORECAST puts a defensible projection in a cell instead of a chart annotation, which is what a planning model needs. If there is any chance you will reuse this, drop it into a small template tab right now: a labelled input area on the left and the formula beside it, checked once against the tool above. Next time the same question comes up, the answer is a single paste away instead of a rebuild from memory.
In Google Sheets
If you are in Google Sheets rather than Excel, the good news is that the formula shown here is identical and the workflow barely changes — menus sit across the top instead of in a ribbon, and a few function names differ slightly, but anything you build here moves across with little or no rework. Nothing on this page is behind a login or a download: the exact answer is at the top, and the detail below it is there for when you need it. That is the whole promise here — the answer first, and just enough context to make it stick. The short version of “forecast formula excel”: the answer is at the top of this page, the tool proves it on your own numbers, and the sections above explain why it holds so the next variation does not stump you. Excel rewards people who reference cells instead of typing values and who keep inputs separate from formulas, because that is what makes a result you can audit months later. Build it once, deliberately, with the live tool as a check, and you convert a one-off lookup into a reusable skill — which is the whole point of learning the why and not just the what.
Common mistakes
- Predicting far outside the range of the historical x values, where the fitted line carries no evidence.
- Using the linear form on a seasonal series; FORECAST.ETS exists for that and needs evenly spaced dates.
- Mixing up the argument order — the x to predict comes first, then y values, then x values.
Frequently asked questions
What is the difference between FORECAST and TREND?
FORECAST returns one predicted value; TREND returns a whole array of them, and also supports multiple independent variables.
When should I use FORECAST.ETS?
When the data is a time series with a repeating seasonal pattern and evenly spaced dates. The linear form cannot represent seasonality.
Is FORECAST the same as SLOPE plus INTERCEPT?
Yes — =FORECAST.LINEAR(x,ys,xs) equals =INTERCEPT(ys,xs)+SLOPE(ys,xs)*x exactly.
Other ways people ask this
On the way here you may have searched this as “how to use forecast in excel”, “forecast spreadsheet excel” and “forecast using excel” — it is all the same task, and this page is the single, complete answer to it.
Why do people search for this in so many different ways?
Because the same task has many names. “how to use forecast in excel”, “forecast spreadsheet excel”, “forecast using excel” all point at the one operation explained on this page, which is why they all lead here.