Billable Hours to Invoice Period Calculator
Turn the billable hours you log each week into an invoice total for a date range — with hours, subtotal, tax and the amount due.
How it works
weeks = (days in period ÷ 7) counting both end dates · billable hours = hours per week × weeks · subtotal = hours × rate · amount due = subtotal × (1 + tax%)
This converts a steady weekly billing pace into the invoice for a specific date range. The period length is counted inclusively of both the start and end dates, divided by seven to get the fractional number of weeks, then multiplied by your billable hours per week and your rate. Any tax or GST is applied to the subtotal to give the final amount due, so a month that spans slightly more than four weeks bills proportionally more than a flat 4-week assumption would.
Worked example
September 1–30, 2026 is 30 days, or about 4.29 weeks. At 25 billable hours a week that is roughly 107 hours; at $75/hour the subtotal is about $8,036, and with no tax the amount due is the same.
Frequently asked questions
Does the period include both the first and last day?
Yes. The day count is inclusive of both the start and end dates, so September 1 to September 30 counts as 30 days, not 29. That is the usual convention for a billing period.
What if I only work certain days?
Enter your true billable hours per week rather than hours per day. The tool spreads that weekly figure across the exact number of weeks in the range, so occasional days off are already baked into your weekly average.
Should I bill for non-billable admin time?
No — enter only the hours you actually invoice a client for. If you want to see your billable share of total hours worked, a utilization-rate calculator handles that separately.
Related calculators
Estimate only — confirm rates, hours and applicable taxes against your contract and local rules before invoicing.