What this site does. You bring a table of numbers, it gives you
numbers back. This page fits a straight line or a polynomial to each column by
least squares - the coefficients that make the vertical misses smallest - and
gives you the equation, R², RMSE and the residuals. It runs entirely in your
browser — nothing is uploaded, nothing is stored. If you want the reasoning
rather than the answer, the curve fitting
article explains every model on a worked example.
A high R² does not make a model right: look at the residual chart. A pattern
in it - a U, a trend - means the wrong model. Exponential, power, logistic and
Gaussian models are on the advanced
calculator.
- Paste your data into the Input grid — straight from a
spreadsheet, or as CSV/TSV text — or import a CSV/TSV file.
Column x, then up to three y columns. Up to 5,000 rows.
- A row with no number in x is skipped; a blank y cell is skipped for that
column only. Each column is fitted on its own, and needs at least as many
points - at different x - as the model has coefficients.
- Pick a method.
- linear: a straight line, y = a + b·x.
- polynomial: a line plus powers of x, y = c0 + c1·x +
… + cn·xⁿ. The order n sets how many bends the curve may have.
- Set the order (polynomial only): 1 to 10. Order 1 is the
straight line. Use the lowest order that leaves no pattern in the residuals;
an order of one less than the number of points passes through every point,
which is interpolation, not a fit.
- Real time range — try orders live on the order box.
- ▲▼ buttons or the mouse wheel over the
box: the order moves and the fit is recomputed at once - no need to
press fit.
- Limits: order 1 to 10; a typed value outside is set to
the nearest limit.
- Typing or the arrow keys change the box only; press
fit to recompute.
- Press fit. The status line gives R² for each column. The upper
chart shows your data as dots and each fitted curve as a line in the same
color; the lower chart shows the residuals - each point's vertical miss.
- Read the result. Under the charts, pick a column: R², adjusted
R², RMSE and points on the first line, the equation, ready to retype, on the
second. See more - hover or click - shows a line cut short and
any note. The Output grid
lists x, then for each column the fitted y and the residual.
Export saves it as a CSV/TSV file.