Front end estimation mostly produces a closer estimate of sums or differences than the answer produced by adding or subtracting rounded numbers.

How to estimate a sum by front end estimation:

Add the digits of the two highest place values
Insert zeros for the other place values

Example 1: 4496 + 3745 is estimated to be 8100 by front end estimation (i.e. 4400 + 3700).
Example 2: 4496 + 745 is estimated to be 5100 by front end estimation (i.e. 4400 + 700).