How much fuel to carry?

[Keith Smith]

A few people expressed concern regarding the decision to carry 2hrs 15mins of fuel for a 28-minute IFR flight. There are 3 approaches to fuel planning:
1) carrying enough to be legal
2) carrying enough to be practically safe
3) full fuel, no matter what

Really, it's a spectrum, rather than just 3 discrete points, but you get the idea.

I subscribe to approach #2. It has little to do with performance (the extra weight hurts the climb a little bit, but not much on the cruise speed) but everything to do with convenience. I fly the plane because of the utility it affords. Adding 20 minutes to the start of every flight to start up, taxi to the pumps and fill up would eat up a lot of time over the course of many flights.

I weigh the likelihood of needing to divert, and how far the diversion will realistically be and then I make a decision as to how much fuel needs to be on board.

On a recent trip (Florida to DC), I planned two versions of the flight, one with a fuel stop and one without. The winds aloft ended up being exactly as forecast with the strong tailwind resulting in me being able to do the flight non-stop, but had they not panned out, I'd already worked out a no-brainer fuel stop with favorable pricing and weather.

How do you approach fuel planning?