The taper is fixed before you start
If the room is an inch wider at one end than the other, an inch of taper is going into the floor. Nothing about how the first row is laid changes that, because the rows are straight and the walls are not. All the layout decides is which row carries it and whether it gets halved.
That is why the page prints three versions of the same job. Run the first row tight to the starting wall and the whole taper lands in the last row against the far wall. Scribe the first row instead and the same taper moves to the near wall, where it may be less visible or more. Split it and two rows each carry half, which is the version that keeps both rips furthest from being too narrow to lay.
Half a taper is not half a problem, it is a different one
Splitting looks obviously better and often is, but it has a cost: the rows no longer run parallel to any wall. Every board sits at a slight angle to the baseboard on both sides, which is invisible at a quarter degree and is not at two degrees. In a room with a strong reference line — a run of cabinets, a hearth, a long straight wall — running parallel to that line and dumping the taper against the opposite wall usually looks better than splitting, even though the arithmetic prefers the split.
Whether the rip has to be tapered at all
The page divides the taper by the run and multiplies by the plank length. If a single board only changes by a couple of hundredths across its length, that row can be ripped square, board by board, at a slightly different width each time, and the tiny steps between boards disappear under the shoe. If it changes by an eighth, it is a tapered cut, marked at both ends and cut to the line, and the whole row has to be dry-laid first.
Out of parallel and out of straight are different faults
Two measurements find a wall that is not parallel. They cannot find a wall that bows, and old walls usually do both. A quarter inch of belly in the middle of a fourteen foot wall produces a scribe that neither end measurement predicts, and a first row cut to the two end figures will show a gap in the middle that the baseboard has to cover. Run a string line before committing.
Questions people ask
My room is an inch out of square, is that a problem?
It is normal, and it is only a problem if the taper ends up somewhere visible or if it makes a row too narrow to lay. An inch over eighteen feet is about a quarter of a degree, which nobody sees in the boards themselves; what people see is a last row that goes from three inches down to two along a wall they walk beside. Move it or split it and the same inch stops being noticeable.
Should I split the taper between the first and last row?
Usually, and especially when one row would otherwise come out too narrow to lock. The trade is that the rows then run parallel to neither wall, so every board sits at a slight angle to both baseboards. In a room with a strong straight reference — cabinets, a hearth, a long unbroken wall — running parallel to that and putting the whole taper against the opposite wall often looks better.
How narrow can the last row be?
That is a product limit rather than a general one, and it is worth reading before the first row goes down. Many click products state a minimum width because a rip that goes past the groove has no locking profile left on that edge, so it has to be glued and weighted instead of clicked. The field on this form is for your own limit, and the instructions for the product you bought are the authority on theirs.
Do I measure to the wall or to the baseboard?
To the finished wall face, and to the same reference at both ends. If the baseboard is staying on, measure to the wall behind it or to the bottom of the baseboard consistently, because a baseboard that is thicker at one end will invent a taper that is not there. The expansion gap then comes off both sides before any of the row arithmetic starts.
Does being out of square change how much flooring I need?
Barely. The area is almost the same and the row count usually does not move, so the box count from an ordinary flooring calculator still holds. What changes is where the cuts fall and how much of the tapered row becomes offcut, which is a few boards rather than a few boxes.