How do I calculate a forcing sequence without blundering?
These answers restate the rules implemented by our open-source engine, which follows the WXF laws and is regression-tested against the official 110-diagram repetition casebook. Where an answer refers to a specific position, that position lives on the linked reference page, where the build verifies it against the engine before publishing.
Direct answer
At every step, list the opponent's checks, captures and threats before choosing your own next move. Most calculation errors are not failures to see far enough; they are failures to check the forced replies at a step in the middle, which is where an assumed "only move" turns out to have a second option that ruins everything.
Check their resources at every step, not just the first
It is easy to calculate the opponent's best reply to your first move and then relax. Do the same check at every subsequent move in the sequence: a capture, a check or a counter-threat you missed halfway through can undo a line that looked completely winning at move one. This is the same failure described in why tactics get missed, just one step further into the calculation.
Confirm the final position, not just the material count
Reaching a line where you are ahead on material is not the same as reaching a position that is actually winning. Look at the resulting position specifically: are your pieces safe, is your own palace still covered, and can the opponent's remaining pieces create a problem of their own.
Related questions
How many moves ahead should I calculate?
As far as the position is forcing, and no further. Once a move is not forced, the calculation branches too much to be reliable by hand.
Should I trust my first instinct in a forcing line?
Verify it rather than trust it. The two-question habit, what did their last move attack and what does mine give up, catches most of what instinct misses.
.