Billable Hours Calculator

Billable hours are time logged against a client engagement, multiplied by the agreed rate. Overtime kicks in past a contractual threshold (commonly 40/week) at a multiplier (1.5x or 2x). Discounts apply as a percentage off the subtotal, before or after tax depending on the contract.

The calculator takes regular hours, overtime hours, rate, multiplier, and any discount, returning an itemized invoice total.

Billable hour conventions vary by industry. Law firms standardized on 1/10-hour (6-minute) increments mid-20th century, with the convention that any task less than 6 minutes still bills 0.1 hours. IT consulting and creative agencies commonly use 15-minute or 30-minute increments. Engineering and architectural firms often bill in 6-minute increments for engagements with detailed time tracking, longer increments for fixed-fee projects. The math is straightforward: total = (regular hours × rate) + (overtime hours × rate × multiplier), with discount applied as a percentage of the subtotal. Tax handling depends on jurisdiction — services are mostly tax-exempt in the US at the state level (with exceptions in Hawaii, New Mexico, South Dakota, and West Virginia), VAT-applicable in the EU, and GST-applicable in Canada and Australia.

A worked example: a contract specifies $150/hour for the first 40 hours weekly, 1.5x for overtime. Logged 45 regular and 8 overtime hours. Regular total: $6,750. Overtime total: 8 × $150 × 1.5 = $1,800. Subtotal: $8,550. Apply a 10% discount for early payment: $7,695. Add 8% sales tax (in a tax-applicable jurisdiction): $8,310.60 final. The calculator returns each line so the client can verify. Common variants: separate rates for different work types (design vs. development), a not-to-exceed cap, retainer credits applied against billable amounts.

Limitations: the calculator handles arithmetic, not contract interpretation. Whether overtime applies to time over 40/week, 8/day, or some other threshold depends on the agreement. Whether the discount applies pre- or post-tax matters for the final amount. International work raises currency questions the calculator doesn't address. Time tracking accuracy is the elephant in the room — billable hour disputes nearly always come down to "did this task really take that long" rather than the math. Keep contemporaneous records (calendar entries, commits, status updates) so logged time can be defended on review.