A budget is essential, but it is not designed to predict the future perfectly.
Most companies prepare their annual budget before the year begins. It reflects management’s expectations at that point in time: planned sales, marketing investment, hiring, operating costs, inventory requirements and cash needs.
The problem is that the business environment does not remain static.
Customer demand changes. Marketing campaigns perform differently from expectations. Average order value moves. Supplier prices increase. Inventory arrives earlier or later than planned. As a result, a budget that was reasonable in January may already be outdated a few months later.
This is why companies need a rolling forecast.
Budget and forecast serve different purposes
A budget establishes the company’s original financial commitment and performance target. It provides a baseline against which management can measure results.
A rolling forecast serves a different purpose. It answers:
Based on what we know today, what is now likely to happen?
The budget should normally remain fixed so that management can evaluate performance against the original plan. The forecast, however, should be updated whenever new actual results and business information become available.
In my e-commerce FP&A model, I maintained separate views of:
- Actual performance
- Original budget
- Latest forecast
- Actual-versus-budget variance
- Actual-versus-forecast variance
This makes it possible to preserve accountability while also giving management a realistic forward-looking view.
Updating the forecast with actual performance
Each month, the completed period is replaced with actual results. The remaining months are then reassessed using the latest operating drivers.
For an e-commerce company, this means updating more than revenue alone.
The main forecast drivers include:
- Orders by acquisition channel
- Average gross and net order value
- Product and channel mix
- Return rates
- COGS and gross margin
- Marketing expenditure
- Outbound freight cost per order
- Inventory days and purchasing requirements
- Accounts receivable and payable assumptions
- Fixed operating costs
- EBITDA and ending cash
For example, lower-than-expected orders do not automatically mean that every future month should be reduced by the same percentage. Finance should first understand the underlying cause.
Was traffic below plan? Did conversion decline? Was a promotion ineffective? Did average order value fall because customers purchased lower-priced products? Was the variance temporary, or does it reflect a structural change in demand?
The forecast should reflect the answer.
Why an 18-month rolling view is useful
My model extends beyond the current financial year, creating an approximately 18-month forward-looking view as the forecast rolls forward.
This is particularly useful because many business decisions extend beyond December.
A company may need to consider:
- Inventory purchases with long lead times
- Warehouse capacity
- New employees and salary commitments
- Marketing investment
- Supplier negotiations
- Cash requirements
- Expansion plans
A forecast that ends at the financial year-end can hide important consequences that occur in the following year.
For example, additional inventory purchased in December may support future growth, but it may also reduce cash before the related revenue is generated. An extended rolling forecast makes this timing visible.
A forecast should connect operations, profit and cash
One of the most important lessons from building the model was that revenue forecasting cannot be separated from inventory and cash planning.
The relationship is connected:
Orders and AOV
→ Revenue
→ Product demand
→ Purchasing and inventory
→ COGS and gross profit
→ Operating expenses
→ EBITDA
→ Working capital
→ Ending cashA forecast can show revenue growth and improving EBITDA while still identifying future cash pressure caused by inventory purchases or payment timing.
That is why management should not rely only on the income statement.
The real value of rolling forecasting
A rolling forecast is not simply a spreadsheet that is updated every month. Its value lies in supporting better decisions.
It helps management answer:
- Are we still likely to achieve the annual target?
- Which assumptions are no longer realistic?
- Where are the main risks and opportunities?
- Should marketing investment be reallocated?
- Do we need to adjust purchasing or inventory levels?
- Can the business fund its growth plan?
- What actions are required now?
A budget tells the business where it originally intended to go.
A rolling forecast shows where the business is currently heading—and gives management time to change direction.