Slope and intercept in Excel

A great deal of financial analysis is the claim "y moves with x" made precise: sales with footfall, cost with volume, a stock's return with the market's. The tool is ordinary least-squares regression. It fits the straight line y = m·x + b that minimises the sum of squared vertical distances from the points to the line. The slope m is how much y changes per one-unit change in x. The intercept b is the fitted y when x = 0. Excel hands you each one without a chart:

SLOPE(known_ys, known_xs)        →  m
INTERCEPT(known_ys, known_xs)    →  b
FORECAST.LINEAR(new_x, known_ys, known_xs)  →  b + m·new_x
TREND(known_ys, [known_xs], [new_xs])       →  fitted/forecast y (spills for many new_xs)

Watch the argument order. SLOPE and INTERCEPT take the y's first, then the x's. That's the reverse of how you say "x versus y," and it's a frequent source of an upside-down slope. FORECAST.LINEAR puts the new x first, then the y's, then the x's. It's the M365 name, and the bare FORECAST still works but is deprecated. TREND is the array-spilling generalisation. Give it a column of new x's and it returns the whole column of predictions at once.

How do you interpret a slope and an intercept?

The skill here is interpretation. Getting the formula right is the easy part. A slope of 2.55 on sales (₹ thousands) against footfall (thousands of visitors) means each additional thousand visitors is associated with ₹2,550 more weekly sales. Lean hard on the word "associated." The regression measures co-movement, and it doesn't measure cause. An intercept only means something if x = 0 is a sensible, in-range scenario. "Sales at zero footfall" is a nonsense extrapolation for a shop that's never empty, so you report the intercept as a fitting constant and don't call it "base sales." Reading FORECAST.LINEAR(30, …) off the line at footfall = 30 is legitimate, because 30 lies inside the observed range. FORECAST.LINEAR(200, …) would be extrapolation into territory the data never saw, and the limitations of regression analysis page warns against that.

Where are SLOPE and INTERCEPT, and how do you check them?

These are under Formulas ▸ More Functions ▸ Statistical (Alt, M, Q, then S). For a quick visual, select the x and y columns and press Alt+F1 to drop a chart. Then go to Chart Design ▸ Add Chart Element ▸ Trendline ▸ More Options and tick "Display equation" and "Display R-squared". The equation's slope and intercept must match your SLOPE/INTERCEPT cells digit for digit. Checking that is a good reconciliation habit.