EOQ with Discount Calculator

How to Use This Tool

Follow these steps to calculate your optimal order quantity with bulk discounts:

1. Enter your annual demand for the product in units per year.
2. Input the fixed cost per order (including shipping, processing, and administrative costs for each purchase order).
3. Select your holding cost type: percentage of unit cost (common for retail) or fixed amount per unit per year (common for warehousing).
4. Enter the holding cost value corresponding to your selected type.
5. Fill in the three price break tiers with minimum order quantities and discounted unit prices. Ensure each tier has a higher minimum quantity and lower unit price than the previous tier.
6. Click Calculate Optimal EOQ to see your results.
7. Use the Reset All button to clear all inputs and start over.

Formula and Logic

The calculator uses the standard Economic Order Quantity (EOQ) model adjusted for quantity discounts. The core EOQ formula calculates the order quantity that minimizes total inventory costs without considering discounts:

EOQ = √(2DS / H)

Where:

• D = Annual demand (units/year)
• S = Ordering cost per order ($)
• H = Holding cost per unit per year ($)

For discounted pricing, the tool evaluates each price break tier: it calculates the EOQ for each tier's unit price, checks if the EOQ falls within the tier's quantity range, then computes total annual cost (purchase + ordering + holding) for all feasible quantities. The optimal order quantity is the one with the lowest total annual cost across all tiers.

Total Annual Cost = (D × P) + (D / Q × S) + (Q / 2 × H)

Where P is the unit price for the selected tier, and Q is the feasible order quantity.

Practical Notes

These business-specific tips will help you apply results to real-world operations:

• Ordering costs should include all expenses for processing a purchase order: labor, shipping, inspection, and administrative fees. Exclude costs that don't change with order quantity.
• Holding costs typically range from 20-30% of unit cost for retail goods, covering warehousing, insurance, obsolescence, and capital tied up in inventory.
• Price breaks often have hidden costs: higher order quantities may require more warehouse space, increase risk of unsold stock, or tie up cash flow. Always evaluate non-cost factors alongside the calculation.
• For e-commerce sellers, factor in platform fees and shipping costs to customers when setting price break thresholds.
• If your supplier offers more than three price breaks, you can adjust the calculation by adding more tiers to the underlying logic (the current tool supports three tiers for most common bulk discount structures).

Why This Tool Is Useful

Small business owners, traders, and e-commerce sellers face a constant tradeoff: ordering more units to get bulk discounts increases holding costs, while ordering less reduces holding costs but raises purchase and ordering expenses. This tool eliminates guesswork by:

• Balancing all three core inventory cost components automatically
• Comparing total costs across all discount tiers to avoid over-ordering for small discounts
• Providing a detailed cost breakdown to support supplier negotiations
• Helping you maintain healthy cash flow by avoiding excess inventory stockpiling

Frequently Asked Questions

What if my supplier offers more than three price breaks?

The tool is preconfigured for three common discount tiers, which cover most bulk pricing structures. For additional tiers, you can export the calculation logic and add more price break rows following the same validation rules (increasing minimum quantities, decreasing unit prices).

How do I calculate holding cost as a percentage?

Add up all annual holding expenses (warehousing rent, insurance, labor, obsolescence, opportunity cost of tied-up capital) for a single unit, divide by the unit's cost, and multiply by 100. For example, if holding a $10 unit costs $2 per year, the holding cost percentage is 20%.

Can I use this for perishable goods?

This tool assumes non-perishable inventory with constant demand. For perishable goods, you should adjust the holding cost to include spoilage losses, or use a specialized perishable inventory calculator that accounts for shelf life.

Additional Guidance

To get the most accurate results, update your inputs quarterly to reflect changes in supplier pricing, shipping costs, or warehouse expenses. Always cross-verify the calculated optimal order quantity with your supplier's minimum order requirements and your available warehouse capacity. If you have seasonal demand fluctuations, run separate calculations for peak and off-peak periods to adjust ordering strategies throughout the year.