This article explains how % TM Leverage is calculated in SDL TMS.

Keep in mind the following:

• % TM Leverage = [Total Weighted Word Count]/[Word Count]
• [Weighted Word Count] = [Words Per Band] * [Lower Bound of Band]: the weighted word count is calculated for each band as the actual word count times the lower bound of the band. 
• Repetitions are treated as 100% matches.
• The total of the weighted word counts is divided by the word count to yield the percent translation memory leverage.

For example:
 

Bands	Words per band	Lower bound of band	Weight word count
Repetitions	21	100%	21
100%	24	100%	24
99% - 85%	64	85%	54.4
84% - 75%	6	75%	4.5
74% - 0%	137	0%	0
TOTAL	252		103.9

% TM Leverage = [Total Weighted Word Count]/[Word Count]
% TM Leverage = (103.9 / 252) = 41.23%

Finding % TM Leverage in the SDL TMS User Interface:

Open a Job Summary page. 
Under the Linguistic Analysis section, click on a Language Pair. 
This will open the Cost Banding page for that language pair; the top section of the page, Cost Band Word Counts, will show % TM Leverage on the left.