timecard-engine

Zero-dependency time card & timesheet calculation engine for JavaScript — the same engine that powers timecardcentral.com.

• Worked hours from punch times, with overnight shifts, multiple break spans, and break clamping
• Rounding: 7-minute rule (nearest 15), 15-minute truncation, hundredths — applied to punches and/or totals
• Overtime: FLSA weekly OT (per workweek, weighted-average regular rate) and California daily OT/DT (8/12 split, 7th-consecutive-day rules)
• Gross pay: per-day rates, weekly weighted regular rate, OT/DT premiums
• Conversions: decimal hours ⇄ clock time, 12-hour ⇄ military time, salary ⇄ hourly
• Extras: OBBBA "no tax on overtime" deduction estimator, marginal bracket tax, FLSA weighted-overtime breakdown

Pure ESM, no dependencies, runs on Node ≥ 18 and in browsers. Ships a timecard CLI.

npm install timecard-engine

Library usage

One day: punches, breaks, rounding

import { computeDayMinutes } from "timecard-engine";

const day = computeDayMinutes({
  in: "8:30am",
  out: "5:15pm",
  breakStart: "12:00",
  breakEnd: "12:45",
});
// => { worked: 480, span: 525, breakMin: 45, ok: true, ... }   8h worked

// overnight shift + minute deduction + 7-minute punch rounding
computeDayMinutes(
  { in: "22:00", out: "06:30", breakMinutes: "30" },
  { rounding: { mode: "7min", applyTo: "punches" } }
);

A full pay period: FLSA overtime and gross pay

import { computePeriod } from "timecard-engine";

const days = [
  { in: "9:00", out: "18:00", breakMinutes: "60" }, // Mon 8h
  { in: "9:00", out: "18:00", breakMinutes: "60" }, // ... 5 x 8h
  { in: "9:00", out: "18:00", breakMinutes: "60" },
  { in: "9:00", out: "18:00", breakMinutes: "60" },
  { in: "9:00", out: "18:00", breakMinutes: "60" },
  { in: "8:00", out: "12:00", breakMinutes: "0" },  // Sat 4h  -> 44h week
];

const r = computePeriod(days, { hourlyRate: 20 });
// r.totalHours = 44   r.otHours = 4
// r.regularRate = 20  r.basePay = 880  r.otPay = 120  r.grossPay = 920

FLSA semantics are modeled properly:

• overtime accrues per workweek (a biweekly period is two workweeks — 29 U.S.C. §207(a)(1)), never averaged across the period;
• day-level rates feed a weighted-average regular rate per workweek (FLSA §7(e));
• punch rounding happens before pay arithmetic (29 CFR 785.48(b)).

California overtime (or custom daily thresholds)

import { computePeriod } from "timecard-engine";

const r = computePeriod(
  [{ in: "8:00", out: "18:15", breakMinutes: "15" }],
  { hourlyRate: 20, jurisdiction: "ca" }
);
// 10h day -> r.regHours 8, r.otHours 2, r.grossPay 220  (8×$20 + 2×$30)

CA rules (>8h = 1.5×, >12h = 2×, 7th consecutive day) plus the weekly-OT top-up on top of daily OT, per DLSE methodology. Non-CA employers can pass dailyOtThreshold / dailyDtThreshold instead.

Conversions & helpers

import {
  toDecimalHours, parseClockTime, militaryFull, salaryToHourly,
  hourlyToSalary, weightedOvertime, obbbaDeduction,
} from "timecard-engine";

toDecimalHours(parseClockTime("7:45"));          // 7.75
militaryFull(parseClockTime("18:00"));           // { military: "1800", hhmm: "18:00", h12: "6:00 PM", ... }
salaryToHourly(52000);                           // { hourly: 25, weekly: 1000, ... }
hourlyToSalary(25);                              // { annual: 52000, ... }
weightedOvertime([{ rate: 20, hours: 30 }, { rate: 25, hours: 15 }], 5);
// { regularRate: 21.67, otCompensation: 162.5, grossTotal: 1029.17, ... }
obbbaDeduction(15000, "single");                 // { deduction: 5000, capped: false, ... }

All money-returning functions round to cents; all parsers accept number minutes, "HH:MM", "H:MM am/pm", "HHMM", and lenient money strings like "$1,234.50".

CLI

npm install -g timecard-engine

Command	What it does
timecard day	one work day: punches, breaks, rounding, straight-time pay
timecard period	a full pay period from a JSON or line-format file / stdin
timecard decimal	clock times → decimal hours (--reverse for the way back)
timecard military	12-hour clock ⇄ military time
timecard salary	annual salary ⇄ hourly wage
timecard rounding	print the 7-minute rounding table

Every command takes --json for machine-readable output.

$ timecard day --in 8:30am --out 5:15pm --break 45m --rate 20
Day summary
  Clock in        8:30 AM
  Clock out       5:15 PM
  Shift span      8h 45m
  Break           0h 45m
  Worked          8.00 h  (8h 00m)
  Pay             $20.00/h × 8.00 h = $160.00

$ timecard period examples/week.txt --rate 20
Timesheet — 6 days (examples/week.txt)
  ...
  Total   44.00 h
  Regular 40.00 h   OT 4.00 h   DT 0.00 h
  Gross pay     $920.00

$ timecard decimal 8:30 17:15
8.50  17.25

$ timecard military 1800 6:00pm
1800  =  18:00  =  6:00 PM
1800  =  18:00  =  6:00 PM

timecard period accepts a plain line format — one day per line, in,out[,break][,rate]:

9:00,18:00,60
9:00,18:00,60
8:30am,5:15pm,45m,22.50

…or full JSON (examples/timesheet.json documents every accepted field):

{
  "days": [{ "in": "8:00", "out": "18:15", "breakMinutes": "0", "rate": 20 }],
  "settings": { "hourlyRate": 20, "jurisdiction": "ca", "period": "weekly" }
}

Day fields: in, out, meridiemIn, meridiemOut, breakMinutes, breakStart/breakEnd or breaks: [{start,end}], rate, is7thDay (CA), weekIndex (force workweek assignment). Settings: hourlyRate, period (weekly/biweekly/semi-monthly/monthly), weeklyOtThreshold (default 40), dailyOtThreshold, dailyDtThreshold, jurisdiction (flsa/ca), otMultiplier (1.5), dtMultiplier (2), rounding: { mode, applyTo }, tips.

Rounding modes

Mode	Punches	Totals	Notes
none	as punched	exact minutes	default
7min	nearest 15 min (:00–:07 down, :08–:22 → :15, …)	nearest 15 min	the classic "7-minute rule"
15-down	truncate to quarter hour	truncate	employer-friendly variant
hundredths	unchanged	2-decimal hours	e.g. 8h23m → 8.38 h

applyTo controls scope: punches, total, or both. Rounding is applied to punches before any duration math (29 CFR 785.48(b)); totals-rounding is applied after.

Rule provenance

Calculation rules trace to primary sources, not guesswork:

• FLSA weekly overtime — 29 U.S.C. §207(a)(1)
• Per-workweek weighted-average regular rate — FLSA §7(e)
• Punch-time rounding before pay arithmetic — 29 CFR 785.48(b)
• California daily OT/DT and 7th-day rules — CA Labor Code §510, CA DIR DLSE enforcement policies
• 7-minute rounding table — standard nearest-15-minute punch rounding
• OBBBA overtime deduction (÷3, caps, MAGI phase-out) — IRS 2025 summaries

Disclaimer: estimates for informational use only — not legal, tax, or payroll advice. Compliance depends on your jurisdiction, agreements, and facts; consult a professional for decisions that matter.

Development

npm test    # 53 tests: acceptance cases + CLI integration, zero dependencies to install

Used in production at

TimeCard Central — free browser-based time card calculators (time card, hours, decimal hours, military time, overtime, timesheet templates).

License

MIT