Duration Calculator

📖 Tool Introduction

The Duration Calculator is an online tool built specifically for adding, subtracting and converting spans of time. It removes the kind of mental arithmetic that goes wrong so often in daily life, such as working out how long 8 hours 30 minutes plus 1 hour 45 minutes really is, or by how much your overtime exceeded the original plan. Instead of carrying and borrowing digits on a piece of scratch paper, you simply type two time spans the way you would naturally write them, for example 8h30m, 1:45, or 2d3h5m, and the tool normalizes everything into seconds before adding or subtracting. The answer is then presented both as a clock-style duration and as four separate totals in days, hours, minutes and seconds. Whether you are summing up a project timesheet, totaling shifts in a rota, estimating commute and movie lengths, or comparing two differences, it returns a result accurate to the second within a fraction of a second. The whole process runs locally in your browser, nothing is ever uploaded, and it works equally well on a desktop or a phone, with no sign-up and no installation. Because the parser accepts several natural notations, you do not have to learn a special format: type the way you would jot a duration in a notebook, and the tool figures out the rest. When a subtraction leaves a negative result, the sign is preserved so you can tell at a glance which duration was the longer one, and every figure is rendered with thousands separators and fixed unit labels so the output reads like a clean summary rather than a raw calculation.

✨ Key Features

• Natural-input parsing: understands 8h30m, 1:45, 2d3h5m and bare numbers, recognizing each unit automatically
• Add and subtract modes: switch at the top with one tap; a negative subtraction result shows a minus sign
• Multi-unit result cards: the main answer uses clock notation, and four cards give totals in days, hours, minutes and seconds
• Second-level precision: all arithmetic is carried out in seconds, so carrying and borrowing are handled by code
• One-click copy and download: copy the result into your notes or save it as a text file for timesheet archives
• Fully offline: no network requests and no ad tracking, so sensitive attendance data never leaves your device

📝 How to Use

1. Choose Add durations or Subtract durations at the top
2. Type the first span in the Duration A field, for example 8h30m
3. Type the second span in the Duration B field, for example 1h45m
4. Click Calculate to see the main result and the four unit cards
5. To try another set, click Clear, or click Example to load a demo

⚠️ Notes

• Input format: use notation like 8h30m or 1:45; a bare number is treated as minutes
• Empty fields: if a field is empty or unrecognized, a friendly warning appears instead of a crash
• Negative results: when Duration A is shorter than B in subtract mode, a minus sign precedes the result
• Precision: fractional durations are converted exactly and rounded to the nearest whole second
• Privacy: every calculation happens in your local browser with no network request, so attendance data stays private