Right?

[Thomas]

The calculation itself is pretty straightforward:

Remaining Time = Original Estimate – Time Spent

So in your example:
15 (original estimate) – 6 (time spent) = 9 hours remaining.

If you’re doing this often, a simple spreadsheet (Excel/Google Sheets) works well — just put the two values in cells and use a formula like =A1-B1.

There are also a few online calculators and project management tools that do this automatically if you want something quick without opening a sheet. Tools like Jira, Trello (with plugins), or even basic time-tracking apps will show you remaining time as you log work.

[Pedro Olmo]

Hello @Thomas ,

Welcome to atlassian community!

In Jira, "Time Remaining" is a field automatically calculated from an issue's Original Estimate minus the Time Spent. You can view and adjust this value when you log or edit a worklog entry by entering a specific time for "Remaining estimate" in the log work popup. The accuracy of the "Time Remaining" depends on how the time tracking settings are configured in your Jira instance and how accurately users log their work. 

Understanding the Calculation

• Original Estimate: The initial time you expect to complete a task. 
• Time Spent: The total time that has been logged against the issue in worklogs. 
• Time Remaining: Original Estimate - Time Spent. 

You can ser the next guide to see how to configurate timetracking panel :

https://confluence.atlassian.com/jirasoftwarecloud/logging-time-on-work-items-902499028.html

Regards