health.waiting-time

export function rttWaitingTime(clockStart: string, clockStop: string | null, onDate: string): RttWait

/** The length of an RTT pathway as NHS England reports it. */
export interface RttWait {
  /** clockStop (or onDate while waiting) minus clockStart */
  readonly days: number;
  /** whole weeks waited, days divided by 7 rounded down */
  readonly completedWeeks: number;
  /** n of the reporting time band ">n-1 to n weeks": 0-7 days is 1, 126 days is 18; above 104 is the ">104 weeks" band */
  readonly weekBand: number;
  /** more than 126 days */
  readonly breached18Weeks: boolean;
  /** clockStart + 126 days, the last day still within 18 weeks */
  readonly eighteenWeekDate: string;
  /** whether clockStop was given */
  readonly clockStopped: boolean;
}

import { rttWaitingTime } from "#fune/health.waiting-time@^1";

import { addDays, daysBetween, parseIsoDate } from "./dates_add_days.ts";  ← from dates.add-days ^1.0.0 · built alongside by fune
import { type RttWait } from "./health_waiting_time_types.ts";

/** 18 weeks: a wait of exactly 126 days is still within the standard. */
const EIGHTEEN_WEEKS_DAYS = 126;

/**
 * The length of a referral-to-treatment pathway, counted from the clock start
 * to the clock stop, or to onDate while the patient is still waiting. There
 * are no pauses: NHS England removed them in 2015.
 */
export function rttWaitingTime(clockStart: string, clockStop: string | null, onDate: string): RttWait {
  parseIsoDate(clockStart);
  parseIsoDate(onDate);
  if (onDate < clockStart) {
    throw new RangeError(`onDate ${onDate} is before clockStart ${clockStart}`);
  }
  if (clockStop !== null) {
    parseIsoDate(clockStop);
    if (clockStop < clockStart) {
      throw new RangeError(`clockStop ${clockStop} is before clockStart ${clockStart}`);
    }
    if (clockStop > onDate) {
      throw new RangeError(`clockStop ${clockStop} is after onDate ${onDate}`);
    }
  }
  const days = daysBetween(clockStart, clockStop ?? onDate);
  return {
    days,
    completedWeeks: Math.floor(days / 7),
    // The 0-1 week band holds eight days (0 to 7), every later band seven.
    weekBand: days <= 7 ? 1 : Math.floor((days + 6) / 7),
    breached18Weeks: days > EIGHTEEN_WEEKS_DAYS,
    eighteenWeekDate: addDays(clockStart, EIGHTEEN_WEEKS_DAYS),
    clockStopped: clockStop !== null,
  };
}

Install

fune build

With that line in your source, in a TypeScript project (language typescript in fune.project), fune build resolves it and its 1 dependency, pins them in fune.lock, downloads only the TypeScript package of each, and builds the code above into your project’s .fune/build, one readable file per capability with a header linking back here. Or pin a range in fune.project and build in one step:

fune add health.waiting-time

The manifest, vectors and README with only the TypeScript implementation. Install it without the registry with fune add ./health.waiting-time-1.0.0-typescript.fune, or fetch it from a terminal with fune pull health.waiting-time@1.0.0:typescript.

The whole function, every language, is one file too: health.waiting-time-1.0.0.fune, 16,244 bytes, sha256 198576ddbe1a3d5b288d828d5d7ecf0d8584e072efc036b8df3c44c0abf0be82. It installs into a project of any language.

// fune: before health.waiting-time

// fune: after health.waiting-time

// fune: replace dates.add-days in health.waiting-time

// fune: step health.waiting-time after <n|label>

More from the author

**Week bands.** RTT returns put each pathway in a weekly time band, ">n-1 to n weeks", and `weekBand` is that n. The first band, 0-1 weeks, holds eight days (0 to 7), every later band seven: 8-14 days is band 2, 120-126 days band 18, 127 days band 19. NHS England's last band is "104+ weeks", 729 days and more; `weekBand` keeps counting above 104 (729 days is 105) so a caller can still tell long waits apart, and a return should put anything above 104 in the >104 band. `completedWeeks` is simply whole weeks (days divided by 7, rounded down), for display. A clock that starts and stops on the same day is a real pathway of zero days.

**No clock pauses.** Earlier versions of the rules allowed "patient-initiated clock pauses". NHS England removed them in 2015 with the admitted pathway standard: "there is no longer any provision to report pauses or suspensions in RTT waiting time clocks ... under any circumstances". This capability therefore takes a clock start and an optional clock stop and nothing else, deliberately. Events that the rules do recognise are the caller's to apply:

- a clock stop (rules 4 and 5: first definitive treatment, a decision not to treat, active monitoring, a patient declining treatment, and so on) is the `clockStop` date; - a DNA of the first appointment nullifies the clock (rule 5e, footnote 10), and when the patient rebooks a new clock starts (rule 3e), so pass the rebooking date as a new `clockStart`; - other new clock starts (rule 3: a second bilateral procedure, a new treatment, the end of active monitoring) are likewise new pathways.

**Errors.** A measuring date before the clock start, a clock stop before the clock start, and a clock stop after the measuring date (a stop that has not happened yet) are errors. Dates are ISO `YYYY-MM-DD`, and the measuring date is always an argument, never the clock.

## Source

NHS England, "Recording and reporting referral to treatment (RTT) waiting times for consultant-led elective care", version 5.2, February 2025: section 2.2 reproduces the "Referral to treatment consultant-led waiting times rules suite" (clock starts, rules 1-3; clock stops, rules 4-5), the introduction records the removal of clock pauses, and section 10.1.7 "Measuring the length of RTT pathways" defines the time bands. https://www.england.nhs.uk/statistics/wp-content/uploads/sites/2/2025/10/Recording-and-reporting-RTT-waiting-times-guidance-v5.2-Feb25.pdf

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