Medical Device Lot Start Quantity and Rolled Throughput Yield Calculator
If a work order starts the exact order quantity, it will ship short. Device lines lose units to molding defects, assembly rejects, failed seals, inspection and sterilization, and they must also set aside release samples. This calculator solves for the quantity to start, so the lot ships complete the first time.
Your numbers
Damage, biological indicator and process challenge losses.
Units that will be consumed by release testing and retained, so they cannot ship.
Blended cost at the average point of loss.
Your results
Assumes step yields are independent and applied in series. Use measured first-pass yields from the last several lots, and update the factor if the process changes.
Start quantity vs assembly yield
Sweeps Assembly yield from 85 to 100, holding your other inputs fixed.
Derive yield factors from real lot history
Optional: we can compute step yields from your work order history and suggest planning factors.
Optional. The tool and every export work without this. No spam.
How to use the calculator
Enter the shippable quantity the order needs and the measured first-pass yield for each major step. If your process has more or fewer steps, fold two steps into one yield or set an unused step to 100. Add the units consumed by release testing and retains, a small planning overage, and an average cost for a lost unit. The calculator returns rolled yield, the lot start quantity, expected losses and the dollar cost of yield loss. The sweep shows how sensitive start quantity is to your weakest step.
- Use first-pass yield, not final yield after rework, for each step
- Include sterilization loss even if it is small
- Add release samples and retains because they never ship
- Revisit the overage after every five or ten lots of history
Formula and source
Rolled throughput yield is the product of the individual step yields: RTY = Y1 x Y2 x ... x Yn, a standard Six Sigma and lean metric. The required start quantity is the quantity that must emerge, which is shippable units plus retains, divided by RTY and scaled by the overage. For example, steps at 97, 96.5, 98.5 and 99 percent with 0.8 percent sterilization loss give about 91 percent rolled yield, so shipping 5,000 units with 60 retains needs a start of roughly 5,600 units.
Using the result in your ERP
Most ERPs accept a scrap or yield factor on the item or routing, such as the scrap percent on a BOM component or the yield percent on an operation. Use the start-to-ship ratio as a cross-check on those settings rather than as a replacement. Keep one yield assumption in one place so planners, buyers and costing agree. If actual yield consistently beats the factor, you are over-buying material and over-building. If it falls short, you are shipping partial lots and expediting.
Common mistakes
Averaging yields across different products hides a problem on the one that matters. Using final yield after rework understates the capacity consumed by rework loops. Forgetting that retains and sterilization samples reduce shippable output is another frequent error. For product with a hard cap on quantity, such as a customer-supplied serialized component, the overage may need to be zero and the yield assumption validated tightly. Always treat the result as a plan, then compare to actual lot results.
Frequently Asked Questions
What is rolled throughput yield?
It is the probability that a unit passes through every step without defect or rework, found by multiplying the first-pass yield of each step. It is always lower than the lowest individual step yield, which is why many small losses add up.
Should sterilization loss be included?
Yes, if units can be damaged or consumed during sterilization or handling. Include biological indicator units and any product used for process challenge testing. Even a small percentage matters on a high volume order.
How much overage should I add?
Enough to cover normal variation in yield between lots without building a large surplus. Many planners start at 1 to 3 percent and tune it from lot history. Product with hard quantity caps or expensive components usually needs a smaller cushion.
Can I use this for non-medical products?
Yes. The yield math is general. The medical-specific parts are the retains, release samples and sterilization loss, which you can set to zero for other products.
If you want yield factors derived from actual lot history in your ERP and fed back into planning automatically, that is a task we can help you build.
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