This guide explains the core arithmetic behind the tools. It is intended to help you check assumptions and understand your own pay records, not to provide jurisdiction-specific legal advice.
Midnight is not the end of the shift
A shift from 7 PM to 7 AM is 12 hours long, not a negative time interval. For an end time earlier than the start, add one full day before taking the difference. The Shift Length Calculator handles this automatically.
Subtract only unpaid breaks
A 12-hour shift with a 30-minute unpaid meal break contains 11.5 paid hours. Paid rest breaks generally should not be removed in a planning estimate. Local law and workplace rules control exactly what is compensable.
Night hours are a separate question
A workplace might designate 10 PM to 6 AM as the night window. An 8 PM to 6 AM shift has ten total hours but eight night-window hours. The night premium can apply to only those eight hours.
Consider overlapping premiums
Overtime and night-work premiums may interact in ways specific to the workplace. Some calculations use a blended base rate; others apply different rules. Never assume one global formula when preparing a payroll dispute.