Orignal Estimate - Time spent During in progress = Remaining Estimate

For Example
Orignal Estimate=3h

Spent Time During In progress Status= 2h30m

Then 3h-2h30m=30m 

Means Assignee Completed Task 30 Min Before given estimate

If Time Spent Was 3h20m in previous example then

3h-3h20m= -20m 

Means Assignee Spent 20 min Extra On That Task