Institutional Cost Line — foreign cost basis estimated from official flows, open methodology
"Where is the foreign cost basis?" is a daily question on Taiwan stock forums — but institutions never publish it. We build a volume-weighted estimate from official daily institutional net flows × closing prices over a rolling window, with the methodology fully disclosed and explicitly labelled an estimate — not a mystery "smart money cost" number.
Methodology and limits
Over the last N days (default 60), we take sessions with positive foreign net buying and volume-weight the closing prices by net-buy lots, returning the estimated cost line plus the latest close and its deviation. Deterministic: same data, same result. Honest limit: actual institutional fills are not public — this is a transparent approximation, not ground truth.
What we deliberately do not do
We do not claim this line is a real cost basis. Actual fills, after-hours blocks, FX conversion and hedge legs are all invisible to us; a volume-weighted estimate is the best public-data approximation and is not the number on anyone's book.
We also do not render it as support or resistance, and we ship no 'price broke below the cost line' alerts. It is a line; what to do with it is your call.