MTO growth allowance

Every early MTO under-counts, for structural reasons: routing is preliminary, supports and specials are not yet designed, field adjustments have not happened, and cutting waste is real. Growth allowances compensate — set per material class and per MTO stage, heaviest on early bulk take-offs from P&IDs and preliminary routing, stepping down through the isometric-based MTOs, approaching only cutting and waste margins at the final take-off. Mature organisations calibrate the percentages from their own history of estimated-versus-final quantities rather than from folklore.

The allowance is both necessary and dangerous. Necessary, because procurement of long-lead bulks cannot wait for the design to finish. Dangerous, because a blanket percentage covers whatever is missing without ever identifying it — a systematically under-counting take-off process and a healthy one produce the same-looking numbers until the growth allowance runs out, which it does on site, in the material with the longest lead time. Tracking actual growth against the allowance, package by package, is the only way to tell disciplined take-off from luck.