Interpolate Calculator — Advanced

What this page adds. The basic calculator draws straight lines between your points and never leaves your browser. This page fits curves instead — cubic spline, PCHIP, and Akima — and takes any number of series at once. To do that it sends your table to the server, computes there, and sends the numbers back. Nothing is stored, but the data does leave your machine. If that matters for your data, use the basic page. The interpolation article explains what each method assumes and where each one goes wrong.

1. Paste your data into the Input grid — straight from a spreadsheet, or as CSV/TSV text. First column is x, every other column is a y series. There is no column limit on this page.
2. Or press import to load a file instead. CSV and TSV both work — the separator is detected from the file, so a comma file and a tab file of the same numbers give the same grid. The file is read in your browser and is not sent anywhere.
3. Set the output range. Output X start, finish, and interval decide which x values you get back.
4. Pick a method in the Method select, then press interpolate.
5. Read the result. Values land in the Output grid; the same curves plot under Results.
6. Press export to save the Output grid as a file. The save dialog offers CSV or TSV and whichever you choose decides the separator. On Firefox and Safari the browser cannot offer that choice, so a small CSV/TSV menu appears next to the button instead. Saving happens in your browser; only interpolate talks to the server.

Output x values outside the range of your data are left blank. This interpolates between your points, it does not extrapolate past them.