Git: How to estimate a contribution of a person to my project in terms of added/changed lines of code?

You can use git log and some shell-fu:

git log --shortstat --author "Aviv Ben-Yosef" --since "2 weeks ago" --until "1 week ago" \
    | grep "files\? changed" \
    | awk '{files+=$1; inserted+=$4; deleted+=$6} END \
           {print "files changed", files, "lines inserted:", inserted, "lines deleted:", deleted}'

Explanation: git log --shortstat displays a short statistic about each commit, which, among other things, shows the number of changed files, inserted and deleted lines. We can then filter it for a specific committer (--author "Your Name") and a time range (--since "2 weeks ago" --until "1 week ago").

Now, in order to actually sum up the stats instead of seeing the entry per commit, we do some shell scripting to do it. First, we use grep to filter only the lines with the diffs. These lines look like this:

 8 files changed, 169 insertions(+), 81 deletions(-)

or this:

 1 file changed, 4 insertions(+), 4 deletions(-)

We then sum these using awk: for each line we add the files changed (1st word), inserted lines (4th word) and deleted lines (6th word) and then print them after summing it all up.

Edit: forward slashes were added in the top snippet so it can be copy and pasted into a command line.

You can generate stats using Gitstats. It has an 'Authors' section which includes number of lines add/removed by the top 20 authors (top 20 by commit count).

Edit: There's also Git: Blame Statistics

For particular dates, you can use --since "2012-08-27" --until "2012-09-01"

Like

git log --shortstat --author "Fabian" --since "2012-08-27" --until "2012-09-01" | grep "files changed" | awk '{files+=$1; inserted+=$4; deleted+=$6} END {print "files changed", files, "lines inserted:", inserted, "lines deleted:", deleted}'

Check this explanation

http://gitref.org/inspect/