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@northguild/gmt

Invoice a Day Late

  • Container free time, demurrage, billing deadlines, bill of lading dates and EDI timestamps.

Invoice a Day Late

An invoice issued on day 30 of a 30-day issue window, compared as an instant against a millisecond deadline instead of as a date.

The naive approach

// The naive approach: a 30-day window as milliseconds, compared with an instant
const anchor = new Date("2026-03-01T00:00:00-05:00"); // midnight, 1 March, New York
const deadline = new Date(anchor.getTime() + 30 * 86400e3); // 2026-03-31T05:00:00.000Z
const invoiced = new Date("2026-03-31T09:00:00-04:00"); // 09:00 on day 30
invoiced <= deadline; // false — an invoice on day 30 is flagged a day late

Watch it break

The naive approach silently produces wrong results — there is no GMT equivalent to demonstrate because the failure is not using GMT.

Why

Two mistakes stack. The deadline is a date, not an instant, so comparing an instant with it flags anything issued on the deadline day after the anchor's time of day. And 30 × 86,400,000 ms from a New York midnight crosses the 8 March clock change, so it lands at 01:00 on 31 March, not at midnight. The chain counts dates: day 30 is by the deadline, and day 31 is not.

The gmt approach

import { convertUtcToPlainDate } from "@northguild/gmt/utc";
import { billingTimeline } from "@northguild/gmt/intermodal";

convertUtcToPlainDate("2026-03-31T14:00:00Z", { timeZone: "America/New_York" });
// "2026-03-31"

const windows = { issueDays: 30, disputeDays: 30, resolutionDays: 30 };
billingTimeline({ anchorOn: "2026-03-01", invoiceIssuedOn: "2026-03-31" }, windows);
// { invoiceDeadline: "2026-03-31", issuedByDeadline: true, disputeDeadline: "2026-04-30",
//   requestedByDeadline: null, resolutionDeadline: null }
billingTimeline({ anchorOn: "2026-03-01", invoiceIssuedOn: "2026-04-01" }, windows);
// { invoiceDeadline: "2026-03-31", issuedByDeadline: false, disputeDeadline: "2026-05-01",
//   requestedByDeadline: null, resolutionDeadline: null }

Same widget, working

output 

Change the invoice date to 2026-04-01 and the verdict turns to “after the deadline”: try it in the Billing Deadlines widget. The full rules are in Intermodal: Billing Deadlines.