What is the difference between top-down and bottom-up forecasting, and when would you use each?
A core FP&A interview question — asked in analyst and associate interviews across IB, PE, and the Big 4.
THE SHORT ANSWER
Top-down forecasting starts with a macro target (e.g., total addressable market, company revenue goal) and allocates down to segments or products. It's useful for setting strategic targets or when historical data is scarce. Bottom-up forecasting builds from granular operational drivers (e.g., sales headcount, conversion rates) to aggregate revenue. It's more accurate for operational planning and resource allocation. In practice, I use both: top-down for ambition setting and bottom-up for feasibility analysis, then reconcile the gap.
WHAT INTERVIEWERS LISTEN FOR
- ✓Top-down: macro to micro, driven by market size or strategic goals.
- ✓Bottom-up: micro to macro, driven by operational drivers.
- ✓Use top-down for targets, bottom-up for detailed planning.
- ✓Reconcile both to align strategy with operational reality.
COMMON MISTAKES
- ✗Claiming one is always better.
- ✗Confusing top-down with driver-based modeling.
- ✗Ignoring the need for reconciliation.
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