RunKit + npm: cron-parser

var cronParser = require("cron-parser") const options = { currentDate: new Date("Tue 03 Jan 2017 00:00:00 UTC"), utc: true }; const interval = cronParser.parseExpression("0 30 15 * * 1-6", options); console.log(interval.prev().toDate().toUTCString()); console.log(interval.prev().toDate().toUTCString()); console.log(interval.next().toDate().toUTCString()); console.log(interval.next().toDate().toUTCString()); console.log(interval.prev().toDate().toUTCString());