The Directive does not ask for one number. Article 9 requires seven. This tool computes all seven from a payroll export, flags any category of workers that crosses the five percent threshold in Article 10, and does the whole thing inside your browser.
Nothing you load here leaves this device. There is no upload, no account, and no server involved. The file is read by your own browser, the arithmetic runs on your own machine, and closing the tab erases it. You can disconnect from the internet before you begin and every function below will still work.
Column headers may be in English or Icelandic — Sex or Kyn, Basic pay or Grunnlaun — and either is recognised without configuration. You need one row per employee and, at minimum, a column for sex and a column for basic pay. Columns for variable pay, job category and hours make the report considerably more useful. Export from your payroll system as CSV; nothing needs cleaning first.