Time Duration Calculator

The Problem It Solves

You've worked on a project across four sessions: 2 hours 45 minutes, 1 hour 15 minutes, 3 hours 30 minutes, and 45 minutes. Now the client wants an invoice. What's the total?

Adding time in your head means juggling minutes that spill over into hours, hours that might spill into days, and the constant nagging worry that you carried something wrong. Spreadsheets work but are overkill for a quick calculation. A regular calculator doesn't understand sexagesimal (base-60) arithmetic.

This tool takes any number of time entries, adds them correctly regardless of how large the individual values are, and gives you the total in both HH:MM:SS format and total hours (decimal) for billing.

How the Math Works

The calculation converts everything to seconds, adds them up, then converts back:

Total Seconds = sum of all (Hours × 3600 + Minutes × 60 + Seconds)

Back to display:
Hours   = floor(Total Seconds / 3600)
Minutes = floor((Total Seconds mod 3600) / 60)
Seconds = Total Seconds mod 60

Working in whole seconds avoids floating-point rounding errors. If you enter "90 minutes" in one row, it correctly rolls over to 1 hour 30 minutes in the total — not 90 minutes.

Common Use Cases

Freelance billing: This is probably the most common use. You work in chunks across a day or week — a call here, a design session there. Add each duration with a label, sum them, and you have your billable hours with a clear breakdown your client can see.

Video editing and content creation: Adding up clip durations to plan a video's total runtime, or checking if a sequence of segments fits within a time slot (a 20-minute podcast episode, a YouTube video target, a presentation slot).

Exercise and training logs: Warm-up, main training block, cool-down, stretch — summing all your sessions for the week gives you total training volume.

Study sessions tracking: Using the Pomodoro technique? Log each 25-minute session and see your total focused study time for the day.

Scheduling and event planning: If you're organizing a conference with multiple speakers, add up all the allocated time slots to ensure the total fits within your event window.

Subtitling and transcript timing: Video captioners often need to add up segment durations to sync timestamps correctly.

Features That Make It Practical

Labeled rows: Each time entry can have a description — "Client call," "Code review," "Documentation." This turns th...