Inventory how-to

How to decide if a bulk discount is worth it

A bulk discount is worth it only if the money you save beats the cost of carrying the extra stock until you sell it.

Short answer: A bulk discount is worth it only if the money you save beats the cost of carrying the extra stock until you sell it. Work out how long the bigger order will actually last, add up the carrying cost for that extra time, and compare it against the discount amount.

What "worth it" actually means

A discount lowers your unit cost today. But buying more than you need ties up cash, uses up storage space, and adds risk if the product is seasonal, fragile, or likely to be marked down later. The question is not "do I save money per unit" but "do I save more than it costs me to hold the extra units until they sell".

Work out how long the extra stock lasts

Take your average daily sales for the variant and divide the bulk order quantity by that number. This tells you days of stock. Compare that to your normal order cycle. If a normal order covers 30 days and the bulk deal covers 180 days, you are carrying five extra months of stock to get the discount.

Price in the carrying cost

Carrying cost includes tied-up cash (what else you could do with it), storage space, and the risk of the item going stale, out of season, or discounted later. A simple way to estimate it: take the extra inventory value and apply a monthly carrying cost rate you're comfortable with (many stores use something like 1-2% a month as a rough guide, but pick a number that reflects your own cost of cash and storage). Multiply that by the number of extra months the stock sits around.

Compare the numbers

If the total discount saved is bigger than the estimated carrying cost over the extra holding period, the bulk buy is worth it. If the carrying cost eats most or all of the discount, it is not, even though the per-unit price looks better on paper.

Step by step

  1. Find your average daily sales for the SKU over a recent period, not just last week.
  2. Calculate days of stock for both the normal order quantity and the bulk order quantity.
  3. Work out the total discount in dollars, not just the percentage.
  4. Estimate carrying cost for the extra inventory over the extra days it will sit on the shelf.
  5. Subtract carrying cost from the discount saved to get the real benefit.
  6. Check cash flow: can you afford to pay for the bulk order and still cover other suppliers and bills.
  7. Check the sell-by or trend risk: is this a product likely to still be wanted in six months.

Worked example

A supplier offers a 10% discount if you order 600 units instead of your usual 100. The unit cost drops from $5.00 to $4.50, saving $0.50 x 600 = $300. You sell this variant at 5 units a day, so 100 units lasts 20 days and 600 units lasts 120 days, meaning you are carrying 500 extra units for about 100 extra days. The extra inventory value is 500 x $4.50 = $2,250. At a 1.5% monthly carrying cost, that's roughly $2,250 x 1.5% x (100/30 months) = about $112 in carrying cost. Since $300 saved is well above $112 in carrying cost, the bulk discount is worth it here.

How SteadyShelf helps

SteadyShelf forecasts daily sales per variant and shows days of stock, so you can quickly see how long a bulk order will actually last before you commit. It does not calculate carrying cost or landed cost for you, so you still need to price that in yourself using your own numbers for cash cost and storage.

$29/month flat, unlimited products and suppliers, 30-day free trial. Run the numbers now with the free reorder point calculator.

SteadyShelf is launching on the Shopify App Store. Join early access to get the install link first.

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FAQ

What carrying cost rate should I use if I don't know mine exactly?

Pick a conservative placeholder, such as 1-2% of inventory value per month, and use it consistently across decisions. It does not need to be perfect. It just needs to stop you from only looking at the discount percentage and ignoring the cost of sitting on stock.

Does a bulk discount make more sense for fast-moving SKUs or slow-moving ones?

Fast-moving SKUs usually make bulk discounts easier to justify, because the extra units sell through quickly and the carrying period stays short. For slow-moving SKUs, the same discount can backfire, since the stock sits for months and the carrying cost can outweigh the savings.

Let SteadyShelf do this math for every SKU

Order-by dates per supplier, seasonal forecasts and draft POs for your Shopify store. $29/month after a 30-day free trial.

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