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Today the Boston Bruins reportedly signed defenceman Zdeno Chara to a seven-year contract that will see him earn an average salary of $6.5 million per season (although his cap hit will be $6.92 million per season until the age of 39, at which point it will drop to $4.0 million) .  Now 33 years old, the deal takes Chara through to the age of 40, almost certainly making this an end-of-career contract.

The contract got me wondering how well defencemen retain their value as they move towards the age of 40.  To try and answer that question, I went to Hockey Reference and took the career performance of every defenceman over the age of 37 to record more than 30 points.  I then took their point totals (adjusted for season) from the age of 30 to 32 to create a starting point, and converted their offensive performance from the age of 33 to 40 to a percentage of their 30 to 32 average.

It was an elite group of players going into the sample: Blake, Bourque, Chelios, Coffey, Galley, Housely, Leetch, Lidstrom, MacInnis, Murphy, Numminen, Schneider, Suter and Zubov.  The following chart shows the results, with the average for each year represented as a black trendline:

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There’s a fairly gradual decrease over the first two years, with most players sticking fairly close to their point totals from the previous three seasons.  After that, there’s a gradual drop-off, from 85% at the age of 35 down to 65% at the age of 40.

Admittedly, this only shows offensive production, but the degradation seems likely to be applicable in other areas of their game as well.  It’s also worth noting that there are exceptions to the rule – Mathieu Schneider was a consistently good offensive defenceman even late in his career, while Nicklas Lidstrom has outperformed the sample by an incredible degree, something I’d be inclined to attribute to his playing style.

I’d guess that Chara falls into the general pattern of the sample, making his contract a decent deal for the next couple of seasons and then turning it into a slight overpay the rest of the way.