Demand Forecast Calculator
Forecast next-period demand with the method you choose: simple moving average, weighted moving average or exponential smoothing.
In short
Formula: SMA = average of entered periods. WMA = Σ(weight × demand) ÷ Σ weights over the last three. SES: Fₜ₊₁ = α × Aₜ + (1 − α) × Fₜ.
What this calculator does
Forecast next-period demand with the method you choose: simple moving average, weighted moving average or exponential smoothing. Worked example, questions and limitations included.
Use it to turn Forecast method, Period 1 actual demand, Period 2 actual demand, Period 3 actual demand (optional), and the other shown inputs into a checked result you can compare, copy, or rerun with different assumptions.
The page shows the formula, a numeric worked example, and the assumptions that affect this supply chain calculation.
Inputs and what they mean
- Forecast method
- — choice value.
- Period 1 actual demand
- — number value.
- Period 2 actual demand
- — number value.
- Period 3 actual demand (optional)
- — number value.
- Period 4 actual demand (optional)
- — number value.
- Period 5 actual demand (optional)
- — number value.
- Period 6 actual demand (optional)
- — number value.
- WMA weight — oldest of last 3
- — number value.
- WMA weight — middle
- — number value.
- WMA weight — newest
- — number value.
- SES smoothing constant α (0–1)
- — number value.
- SES initial forecast
- — number value.
How to use it
- Enter each value in the unit shown next to the box (use the unit converter first if your numbers are in other units).
- Check the breakdown to see every intermediate step.
- Read the limitations before relying on the result.
Formula
Methods as described in Hyndman and Athanasopoulos, Forecasting: Principles and Practice.
You choose the method, weights, α and starting forecast — nothing is assumed.
These methods do not handle trend or seasonality; they lag behind growing demand.
SMA = average of entered periods. WMA = Σ(weight × demand) ÷ Σ weights over the last three. SES: Fₜ₊₁ = α × Aₜ + (1 − α) × Fₜ.
Inputs used: Forecast method, Period 1 actual demand, Period 2 actual demand, Period 3 actual demand (optional), Period 4 actual demand (optional), Period 5 actual demand (optional), Period 6 actual demand (optional), WMA weight — oldest of last 3, and other shown inputs.
Worked example
Six months
- Sum = 680.
- 680 ÷ 6 = 113.33 units.
Reading the result
The headline figure is the main answer. Any breakdown underneath shows the parts that make it up, so you can check the working and see what changes when you adjust an input.
Limitations and assumptions
- No trend or seasonality.
- Six periods maximum.
- No error measure.
- Results are planning estimates built only from the figures you enter. No prices, rates, demand patterns or service levels are built in, and the results are not supplier quotes or carrier rates.
- The result depends on the values you enter for this demand forecast calculator; it does not supply missing rates, rules, prices, dates, or assumptions for you.
Common questions
Which method is best?
The one with the lowest error on your own history. Test them on past periods.
How do I pick α?
Higher α reacts faster to recent changes; lower α smooths noise. Choose by testing on your data.
My demand has seasonality?
These simple methods will miss it. Use a seasonal method validated for your data.
How do I use the Demand Forecast Calculator?
Enter the required values for Forecast method, Period 1 actual demand, Period 2 actual demand, Period 3 actual demand (optional), Period 4 actual demand (optional), and the other fields shown. The calculator applies the formula on this page and shows the main result with any supporting breakdown so you can check the arithmetic.
What formula does the Demand Forecast Calculator use?
SMA = average of entered periods. WMA = Σ(weight × demand) ÷ Σ weights over the last three. SES: Fₜ₊₁ = α × Aₜ + (1 − α) × Fₜ. The visible formula section above lists the calculation path and the edge cases the page handles, so the result can be checked without relying on the form alone.
Can the Demand Forecast Calculator be used for exact decisions?
Use it as a calculation aid, not as a substitute for checking the underlying rule, contract, policy, or professional advice that applies to your situation. When a result depends on local rules, personal details, prices, or dates, enter those values yourself and confirm them before acting.
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