That depends. Different katana from different periods had a different weight distribution. Not all katana were created equal and were custom to the practitioner.

If you are into Kenjutsu you want a blade that has the weight more forward. If you do Iaijutsu then you want the balancing point closer to the tsuba.

Exact location, anywhere from the habaki to 4 inches in front of the habaki. Some people swear by the 1/3 (tsuka part) to 2/3 (blade part).

The word you are looking for is center of balance. As to exactly where I think Liondancer is much more knowledgeable so I'll abstain on that.

I will say though the taper of the blade is much less on the katana than other blades(which gives it the ridged structure along with the folding process and the steel used) So the center of balance is farther out to the tip than is expected of a sword of that size and shape.(Which naturally adds weight to the cuts) This is probably why the blades are rather short for a two handed blade and the handle(tsuka) is so long compared to the size of the blade.

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