Guide
Top-down or bottom-up: two ways to build a plan
One starts from the target and divides it. The other starts from the work and adds it up. Serious portfolios use both, and the gap between them is the information.
A top-down plan starts from the objective — a date, an envelope, a headcount — and divides it across phases and teams. A bottom-up plan starts from the work as the people who will do it describe it, and adds it up. Both produce a number. They almost never produce the same number, and that is precisely what makes running them both worthwhile.
What top-down is good at
Top-down is fast, it exists before anything is known in detail, and it carries the constraint: the market window, the budget voted, the regulatory deadline. It is the only approach that can answer in an hour and the right one for framing, portfolio arbitration and any early comparison between candidate projects. Its weakness is that it is optimistic by construction, because it divides a target rather than measuring an effort.
What bottom-up is good at
Bottom-up is accurate because it is built by the people who will do the work, and it exposes what top-down cannot see: the integration nobody counted, the dependency on a team already busy, the three weeks of environment setup. Its weaknesses are the mirror image: it is slow, it needs a real breakdown, and it drifts upward as each contributor quietly adds their own margin.
The gap is the information
The mistake is picking one and defending it. When the top-down envelope says nine months and the bottom-up sum says fourteen, neither is right — the gap of five months is the message. It says either that the scope carries more than the objective assumed, or that the estimates carry cumulative padding. Investigating that gap is the single most productive conversation of a framing phase, and skipping it is how a project gets committed to a date it never had.
A practical way to combine them
Frame top-down to set the envelope and get the decision. Detail bottom-up on the next horizon only — the coming quarter, the current phase — rather than on the whole project. Then reconcile: what does not fit is arbitrated as scope, not absorbed as overtime. The far end of the plan stays top-down until it comes close enough to be described honestly.
Holding both in FoxPlan
FoxPlan lets a project carry a top-down envelope — budget and capacity set at portfolio level — while the schedule underneath is built bottom-up from tasks and allocations. Both are visible on the same object, so the gap between what was granted and what the plan actually consumes is a number on screen rather than a discovery at the steering committee.
