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What is the difference between fixed-income duration and equity duration?
A bond has a duration that can be easily calculated. It's the time weighted average of all the payments you'll receive and helpful to understand the effect a change in rates will have on that instrument.  The duration of a stock, on the other hand, is a forced construct to then use in other equations to help calculate, say, the summation of a dividend stream. I can calculate the duration of a bond and come up with an answer that's not up for discussion or dispute. The duration of a stock, on the other hand, isn't such a number. Will J&J last 50 more years? Will Apple? Who knows?