Financial planning and analysis (FP&A) is supposed to provide clarity, but in many organizations, it instead becomes a patchwork of outdated spreadsheets, disconnected systems, and well‑intentioned models built on shaky assumptions. Small issues that seem harmless in isolation – like an old Excel file or an outdated KPI – quietly compound until they distort the entire process.
Clean data, consistent KPIs, cross‑functional alignment — I’ve explored the importance of many of these in previous blogs, yet issues continue to surface because FP&A isn’t just about numbers. It’s about the systems, behaviors, and decision‑making habits that shape how those numbers are created and interpreted.
To truly build an effective and successful FP&A team, you first need to learn the most common FP&A mistakes we see and, more importantly, how to avoid them. Only then can your team build a forecasting discipline that’s accurate, adaptable, and aligned with where your business is headed, not just where it’s been.
Mistake #1: Relying on Outdated Excel Files and Disconnected Systems
Here’s a humbling statistic: About 94% of spreadsheets used for business decision-making contain errors, according to a recent study — a rate deemed “concerning” by one of the study’s authors.
These errors happen easily enough: files copied from year to year, spreadsheets passed between teams, manual updates. And while these files often feel “good enough,” they can quietly undermine forecasting accuracy long before anyone notices something is off.
Old Excel files often contain hidden formulas, outdated links, or assumptions no one remembers setting. Version control becomes a guessing game, and your teams likely spend more time reconciling numbers than analyzing them. And when systems don’t talk to each other, your forecast is only as accurate as your weakest data source.
Avoiding this mistake starts with building a single source of truth:
- Integrate systems so data flows automatically.
- Establish governance around how and when information is updated.
- Use FP&A tools that support real‑time collaboration.
Mistake #2: Building Models on the Wrong Assumptions
Just as a new skyscraper won’t be stable if the original blueprints were wrong, even the most sophisticated forecasting model will fail if it’s built on the wrong foundation. Too often, organizations rely on assumptions that were accurate once but that haven’t been revisited in years. Growth rates, cost structures, sales cycles, customer behavior, and operational drivers evolve, yet the model stays the same. When that happens, the numbers may look precise, but they’re not telling the truth.
“But this is the way we’ve always done it,” you might hear, as your team moves forward with assumptions that no longer reflect the business. Then, the true drivers of performance aren’t identified or validated. A model might rely on revenue per unit, for example, when the real driver is utilization. Your forecast then becomes a reflection of past habits and not your current reality.
Avoid this mistake like the plague:
- Assess your key drivers regularly, especially during periods of volatility.
- Document and challenge the assumptions you’re making against historical performance, operational insights, and external trends.
- Encourage cross-functional collaboration with sales, operations, HR, and leadership to ensure the model reflects the business as it truly operates today.
Mistake #3: Overreliance on Historical Data
Historical data is essential, of course, but too often organizations treat last year’s results as a reliable road map for the year ahead, even when the market has shifted dramatically. Then, you find yourself with a false sense of confidence and missing signals that matter, like supply chain disruptions, inflation spikes, regulatory changes, shifting customer behavior, or competitor moves — all of which can render historical patterns irrelevant.
Instead, always work to add context to those historical numbers:
- Incorporate leading indicators (changes in demand, commodity prices, labor availability, industry benchmarks) with qualitative insights from leadership, sales, operations, and external research.
- Test your plan through a scenario analysis.
- Build alternate models that account for potential disruptions or opportunities.
Mistake #4: Using KPIs that Don’t Align with your Strategy
Key performance indicators are supposed to clarify what matters most, so don’t let them become just a long list of metrics that are no longer meaningful. It happens a lot: Teams track what they’ve always tracked, dashboards become cluttered, and leaders end up navigating a sea of numbers that don’t actually reflect strategic priorities. Even worse, if data is pulled inconsistently or from unreliable sources, the KPIs themselves become misleading and create blind spots in the forecast.
Avoiding this mistake starts with focus:
- Identify the KPIs that truly drive performance and tie directly to your strategic objectives.
- Validate that the data behind them is accurate, consistent, and updated automatically.
- Build dashboards around those metrics so everyone is looking at the same indicators and interpreting them the same way.
Mistake #5: Overlooking Workforce Planning in the Forecast
Labor is one of the largest expenses in any organization – up to 70% of a company’s total costs, according to the U.S. Bureau of Labor Statistics – but it’s often overlooked in the forecasting process. Many teams treat it as a static line item rather than a strategic driver that shapes everything from capacity to profitability.
When workforce planning is handled separately from FP&A, the forecast becomes disconnected from the operational realities that determine whether goals are achievable. Planned hires aren’t included in the model, turnover assumptions are outdated or ignored, and merit increases and payroll tax impacts are estimated loosely (or sometimes not at all). So, when leadership is looking to grow (or downsize), the financial implications don’t include enough detail to support confident decision‑making.
Avoid this mistake by treating your workforce planning as a core part of FP&A:
- Model planned hires, start dates, compensation levels, and benefits.
- Incorporate payroll taxes and regulatory changes.
- Include the equipment, software, and workspace required to support new employees.
- Use your forecast to evaluate different staffing scenarios so you can fully grasp how every option affects cash flow, productivity, and your long‑term strategy.
Strong FP&A Requires Structure and Forward‑looking Insight
When organizations move beyond outdated spreadsheets, revisit their drivers, balance historical data with real‑time context, and integrate workforce planning into the forecast, FP&A becomes a strategic engine, not just simply a reporting function.
The organizations that get FP&A right anticipate surprise and use forecasting to understand not just what might happen but what they can do about it. They communicate goals clearly, revisit them often, and ensure every part of the business understands how their decisions shape the financial picture.
If your team is ready to strengthen your FP&A foundation and build a more forward‑looking planning process, MarksNelson can help you get there. Our FP&A experts can help you build the processes that become a source of clarity and confidence, not complexity.
