How ClockSlate works

Calculation Methodology

ClockSlate is designed to make work-time and pay calculations transparent, repeatable and easy to check. This page documents the rules used by version 0.4, last reviewed on September 21, 2026.

Who creates and reviews the calculators

ClockSlate is an independently built utility site. Calculator requirements, formulas, edge cases, copy and release results are checked against documented test cases and representative manual examples. AI-assisted development is used to accelerate research, implementation and testing; it does not replace release review or the published formulas.

Core calculation rules

Clock times and elapsed time

Valid clock times are converted to minutes after midnight. When an end time is earlier than its start time, calculators that support overnight work treat the end as occurring on the next day.

Elapsed minutes = adjusted end − start

Breaks

An unpaid break is deducted after elapsed time is calculated. A break cannot be negative or longer than its shift. Paid breaks are not deducted because they already count toward worked time.

Worked minutes = elapsed minutes − unpaid break minutes

Decimal hours

Decimal hours are a fraction of 60 minutes, not clock-style minutes. The displayed value is rounded to the precision selected by the user, while calculations retain the underlying minute or second value.

Decimal hours = total minutes ÷ 60

Military time

Military-time conversion preserves minutes and maps hours between a 12-hour clock and a 00–23 clock. Midnight is 0000 and noon is 1200. ClockSlate rejects 2400 to avoid treating the end of one day and the start of another as the same calculation value.

Business days and federal holidays

A date counts only when its weekday is selected and it is not a custom exclusion or enabled observed federal holiday. The start date is eligible; the final date follows the visitor's inclusion setting. Adding days treats the start as day zero.

The optional U.S. calendar implements nationwide federal holidays and the standard Monday–Friday observance rule published by the U.S. Office of Personnel Management, reviewed September 21, 2026. It supports 1971 through 2200, excludes state holidays and the location-specific Inauguration Day rule, and falls back visibly rather than silently inventing dates when rules are unavailable.

Pay periods

Weekly and biweekly periods advance by 7 or 14 days. Semimonthly periods use days 1–15 and 16–month end; monthly periods follow calendar months. The day difference from a known period end to a known payday is applied to later periods, then the optional Saturday/Sunday adjustment is applied.

Future payday = future period end + known payday lag

Time rounding

The time-card calculator does not round by default. When selected, each clock-in and clock-out event is rounded to the chosen increment and direction before the shift duration is calculated. Break minutes are not rounded.

Overtime and estimated pay

Regular hours are capped at the user-entered weekly threshold. Hours above that threshold are classified as overtime. A biweekly card evaluates Week 1 and Week 2 separately. Estimated pay multiplies regular and overtime hours by the values entered by the user.

Estimated gross = regular hours × rate + overtime hours × rate × multiplier

Salary conversion

Salary values are normalized to a yearly amount using 12 monthly, 26 biweekly or 52 weekly periods. The hourly equivalent uses the visitor's scheduled hours and paid working weeks.

Hourly equivalent = annual salary ÷ (hours per week × paid working weeks)

PTO accrual

Paid time off can be entered as an annual allowance, a fixed amount per pay period or a rate per hour worked. Starting balance and PTO already used are applied only after earned time is calculated.

Available PTO = starting balance + PTO earned − PTO used

Billable hours

Billable hours are total working hours multiplied by the selected utilization percentage. Estimated collected revenue applies any entered write-off percentage to the gross billed value.

Collected revenue = working hours × utilization × billing rate × (1 − write-off)

Testing approach

Automated tests cover parsing, 12- and 24-hour formatting, midnight boundaries, rounding directions, weekly overtime splits, salary conversion, PTO accrual, billable utilization, business-day ranges and exclusions, observed-holiday boundaries, all four pay frequencies, CSV output, declared routes, canonical sitemap URLs and required assets. Release QA also checks package extraction, JavaScript syntax, security configuration, labels and responsive layout contracts.

Representative cases include 12:00 AM and PM, 0000, compact entries such as 855 and 1730, rejection of 2400, overnight shifts, zero-length entries, breaks longer than shifts, biweekly overtime that must not be averaged, year-crossing business-day arithmetic, leap years, three-paycheck months and negative duration arithmetic.

Privacy and data handling

Live calculations run in the visitor's browser. Calculator entries are not submitted to ClockSlate. Work Settings and time-card drafts are stored in that browser only after an explicit save action. Share links encode selected time-card values in the URL fragment, which browsers do not send to the web server as part of a normal request.

Limitations

ClockSlate does not decide which employment, overtime, break or rounding law applies.
Pay estimates exclude taxes, deductions, benefits, premiums and rules not explicitly entered.
Generated results and spreadsheet templates should be checked against source records before payroll use.
A federal holiday does not mean every employer closes, and a generated pay-period calendar is not payroll advice.
Time zones and daylight-saving transitions are not applied to manually entered clock times.

Corrections and updates

Calculation defects, unclear assumptions and accessibility issues are treated as product bugs. Please contact ClockSlate with the calculator, input values, expected result and observed result so the case can be reproduced.