--- title: "First Pass Yield in CNC Shops: FPY Formula and Fixes" description: "First pass yield (FPY) in CNC shops: the formula, a worked example, how it differs from final yield and scrap rate, and how to improve it." image: https://www.jitbase.com/hubfs/first-pass-yield-fpy-cnc-shops.webp --- [+1 438 942-8501](tel:+1%20438%20942-8501) [Log In](https://app.jitbase.com/) - [English](https://www.jitbase.com/blog/first-pass-yield-fpy-cnc-shops) - [Français](https://www.jitbase.com/fr/blog/first-pass-yield-fpy-atelier-cnc) [![JITbase black logo](https://www.jitbase.com/hs-fs/hubfs/Logos/jitbase-logo-black-horiz.webp?width=175&height=88&name=jitbase-logo-black-horiz.webp)](https://www.jitbase.com) - Solutions Back ##### [Machine Monitoring](https://www.jitbase.com/machine-monitoring) - ##### [Machine Monitoring](https://www.jitbase.com/machine-monitoring) Back - [Live Dashboard](https://www.jitbase.com/machine-monitoring) - [Track OEE](https://www.jitbase.com/machine-monitoring#Track-OEE) - 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[English](https://www.jitbase.com/blog/first-pass-yield-fpy-cnc-shops) - [Français](https://www.jitbase.com/fr/blog/first-pass-yield-fpy-atelier-cnc)   [Book a demo](https://www.jitbase.com/demo) [Connect Machines for Free](https://sso.jitbase.com/realms/webapp/protocol/openid-connect/registrations?client_id=website-registration&response_type=code&scope=openid&redirect_uri=https://admin.jitbase.com) ![CNC operator checking a machined part with a caliper next to a lathe: first pass yield with JITbase](https://www.jitbase.com/hubfs/first-pass-yield-fpy-cnc-shops.webp) Blog [Quality and inspection](https://www.jitbase.com/blog/tag/quality-and-inspection) # First Pass Yield in CNC Shops: FPY Formula and Fixes [*written by* Judicael Deguenon on November 6, 2026](https://www.jitbase.com/blog/author/judicael-deguenon) First pass yield (FPY) is the share of parts that come out of an operation right the first time, with no rework and no scrap. It is also called first time right. It answers a simple question: of everything you started, how much did you get right without touching it twice? Many CNC shops track scrap but not first pass yield. Reworked parts end up in the good count, so the extra machine time, inspection and handling stay hidden. This guide explains the FPY formula and how it differs from final yield and scrap rate. It also shows how to calculate it across several operations, and how to collect the data from the machine and the operator. ## What Does First Pass Yield Measure? First pass yield measures the quality of a process the first time through. A part counts as good only if it passed the operation and its inspection without any rework, adjustment pass or second try. A part that was fixed afterwards may still ship, but it does not count in FPY. In other words, FPY measures how often the shop gets a part first time right. That is what makes FPY useful. Final yield tells you how many parts you shipped. FPY tells you how many you made right. The gap between the two is the hidden factory: the time spent reworking, re-inspecting and rescheduling parts that should have been right the first time. | Metric | What it counts | What it hides | | --- | --- | --- | | **First pass yield** | Parts good the first time, with no rework and no scrap | Whether a part that failed was later saved or lost | | **Final yield** | Parts good at the end, including reworked parts | The time and cost of rework | | **Scrap rate** | Parts lost for good | Every part that was saved by rework | ## The First Pass Yield Formula The formula takes the parts that were good the first time and divides them by the parts that entered the operation: **FPY = (units started − units not right the first time) ÷ units started × 100** Units not right the first time include both the parts that were scrapped and the parts that were reworked. This is a common mistake: if reworked parts are left out, the result is final yield, not first pass yield. ### Worked Example on One Operation A lot of 200 parts runs on a CNC lathe. Inspection finds 12 non-conforming parts: 8 are reworked and shipped, and 4 are scrapped. The numbers are an illustration. | Metric | Calculation | Result | | --- | --- | --- | | **First pass yield** | (200 − 12) ÷ 200 | 94% | | **Final yield** | (200 − 4) ÷ 200 | 98% | | **Scrap rate** | 4 ÷ 200 | 2% | The scrap rate looks fine at 2%, and the final yield at 98%. First pass yield shows that 8 parts went back through rework, each with its own handling, machine or bench time and second inspection. That work is real, but it does not appear in the scrap rate. For the scrap side of the picture, see [reducing scrap rate in CNC machining](https://www.jitbase.com/blog/reducing-scrap-rate-cnc-machining). ## First Pass Yield Across Several Operations Most CNC parts go through more than one operation: turning, then milling, then deburring or a second setup. Each operation has its own FPY, and the yield of the whole route is the product of the yields of each step. This is called rolled throughput yield (RTY). | Operation | FPY | | --- | --- | | Op 10: turning | 94% | | Op 20: milling | 97% | | Op 30: second setup | 99% | | **Whole route** | **0.94 × 0.97 × 0.99 = about 90.3%** | No single operation looks bad, yet about 1 part in 10 needs rework or is scrapped somewhere along the route. On a lot of 200 parts, that is about 20 parts. This is why FPY should be tracked by operation, following the steps in your [manufacturing routing](https://www.jitbase.com/blog/manufacturing-routing-cnc-shop). The route total tells you how much is lost, and the operation tells you where. **Count parts without manual entry.** JITbase reads part counts from the machine, so the number of parts produced is already there when you calculate your yield. [See machine monitoring](https://www.jitbase.com/machine-monitoring) ## What Is a Good First Pass Yield? There is no single target that fits every CNC shop. A shop running short repeat jobs on stable material will not see the same FPY as a shop machining prototypes in hard alloys with tight tolerances. Comparing your number with a figure from another industry tells you little. The most useful reference is your own trend. Track FPY by machine, by part number and by operation, then watch it over several weeks. A stable or rising FPY means the process is under control. A drop on one machine or one part number points to a cause you can find. ## Where First Pass Yield Is Lost in CNC Machining - **The first part after a setup.** Offsets, work coordinates and fixtures are fresh, and the first part is the most likely to be wrong. A disciplined [first article inspection](https://www.jitbase.com/blog/first-article-inspection-cnc-shops) catches the problem before the rest of the lot follows. - **Tool wear.** Dimensions drift as the tool wears, and parts move out of tolerance late in the tool life. - **Offset corrections.** A correction made to save one part can push the next ones out of tolerance if it is not recorded and checked. - **Program changes.** An edit at the machine that is not saved to the master program comes back on the next run of the same job. - **Material and fixturing.** Variation from one bar or one lot of material, or a fixture that does not clamp the same way each time. ## How to Collect First Pass Yield Data FPY needs two numbers per operation: the units started and the units that were not right the first time. The first can come from the machine. The second needs a person, because only an inspection can tell whether a part is conforming. 1. **Count parts from the machine.** An automatic count removes the end-of-shift tally and its errors. See [part counting in CNC shops](https://www.jitbase.com/blog/part-counting-cnc-shops) for how the count is taken. 2. **Declare non-conforming parts at the machine.** The operator records each non-conforming part as soon as it is found, with a reason chosen from a short list. 3. **Count reworked parts too.** A part that is reworked was not right the first time. If operators only declare scrap, your result is final yield. 4. **Keep rework in a separate record if you need final yield.** FPY only needs to know that a part was not right. Final yield also needs to know whether it was saved. 5. **Review by machine and by part number.** A shop-wide average hides the job that causes most of the losses. ![Operator screen next to a CNC machine where non-conforming parts are declared: first pass yield data with JITbase](https://www.jitbase.com/hubfs/JITbase%20on-machine%20display.png) **Give operators a screen at their station.** Operators declare non-conforming parts on the machine screen, and supervisors see them live. [See the operator interface](https://www.jitbase.com/track-manufacturing-operations) ## How to Improve First Pass Yield 1. **Rank the reasons.** Sort non-conforming parts by reason and fix the top one or two first. The method is the same as in [root cause analysis with Pareto charts](https://www.jitbase.com/blog/downtime-root-cause-analysis-pareto-charts). 2. **Secure the first part.** Many losses after a setup can be stopped by checking the first part before the lot runs. 3. **Write down what works.** Record validated offsets, tool life limits and program versions, so the next run starts from a known good state. 4. **Make the change last.** Changes that stick are part of your quality system. See [quality management system examples for CNC machine shops](https://www.jitbase.com/blog/quality-management-system-examples-cnc-machine-shops). 5. **Measure again.** Compare FPY on the same machine and part number before and after the change. FPY is closely tied to the quality factor of [overall equipment effectiveness (OEE)](https://www.jitbase.com/blog/how-to-improve-oee). That factor is usually calculated the same way, good parts divided by total parts, with reworked parts counted as losses. The same data feeds both. ## Where JITbase Fits JITbase reads the part count from the machine, and the operator declares non-conforming parts on the machine screen, with a reason chosen from a list. Together, these give the two numbers that first pass yield needs, by machine and by job, without a paper sheet to fill in at the end of the shift. JITbase does not inspect parts or detect defects on its own: the operator decides whether a part is conforming. It also records non-conforming parts as one category, so if you want to separate rework from scrap to calculate final yield, keep that record in your quality system. What JITbase adds is the data at the machine, so you can see where first pass yield drops, rank the reasons and act on the right job. ## Key Takeaways - First pass yield is the share of parts good the first time, with no rework and no scrap: parts made first time right. - FPY = (units started − units not right the first time) ÷ units started. Reworked parts count as not right. - Final yield and scrap rate can look good while FPY shows a lot of hidden rework. - Across several operations, multiply the FPY of each step to get the yield of the whole route. - Count parts from the machine, declare every non-conforming part at the machine, and review by machine and part number. **See what fewer reworked parts are worth.** Estimate the return of tracking part counts and non-conforming parts on your own machines. [Calculate your return on investment](https://www.jitbase.com/return-on-investment) ## Frequently Asked Questions ### What is first pass yield? First pass yield is the share of parts that come out of an operation right the first time, with no rework and no scrap. It is also called first time right. A part that was fixed after inspection may still ship, but it does not count as good in first pass yield. The metric shows the quality of the process itself, not only the quality of what ships. In a CNC shop it reveals the time spent reworking and re-inspecting parts, which scrap rate and final yield do not show. ### How do you calculate first pass yield? Take the units that entered the operation, subtract the units that were not right the first time, then divide by the units that entered. For example, if 200 parts are started and 12 are non-conforming, first pass yield is 188 divided by 200, or 94%. The units that were not right include both scrapped parts and reworked parts. If you only subtract scrap, you get final yield instead, and the result will look better than the process really is. ### What is the difference between first pass yield and final yield? Final yield counts the parts that are good at the end, including parts that were reworked. First pass yield only counts the parts that were good the first time. In the example of 200 parts with 8 reworked and 4 scrapped, final yield is 98% while first pass yield is 94%. The gap between the two is the rework load. A shop with a high final yield and a much lower first pass yield is shipping good parts. It is paying for them with extra machine time, handling and inspection. ### Does a reworked part count in first pass yield? No. A reworked part was not right the first time, so it counts against first pass yield, even if it ships after the repair. This is the main difference between first pass yield and final yield. In practice, this means operators must declare reworked parts as non-conforming, not only scrapped parts. If rework is fixed quietly at the bench and never recorded, first pass yield will look higher than it really is. ### What is rolled throughput yield? Rolled throughput yield is the first pass yield of a whole route of operations. You calculate it by multiplying the first pass yield of each operation. Three operations at 94%, 97% and 99% give a rolled throughput yield of about 90.3%. It shows how much is lost across the full route, even when each operation looks acceptable on its own. To know where to act, keep the first pass yield of each operation as well. ### What is a good first pass yield for a CNC shop? There is no universal target. The right level depends on the parts, the material, the tolerances and the size of the lots. A shop running repeat jobs will not reach the same number as a shop machining prototypes in hard alloys. The best reference is your own trend by machine, part number and operation. Set a baseline over a few weeks, fix the top causes of non-conforming parts, and check that first pass yield rises and stays stable. #### SHARE [mailto:email@example.com?subject=Mail%20from%20our%20Website](mailto:email@example.com?subject=Mail%20from%20our%20Website) ## Related Articles [![CNC machinist checking a part with a caliper next to a machine: quality management system examples with JITbase](https://www.jitbase.com/hs-fs/hubfs/quality-management-system-examples-cnc-machine-shops-hero.webp?width=352&name=quality-management-system-examples-cnc-machine-shops-hero.webp)](https://www.jitbase.com/blog/quality-management-system-examples-cnc-machine-shops) [Quality and inspection](https://www.jitbase.com/blog/tag/quality-and-inspection) ### [Quality Management System Examples for CNC Machine Shops](https://www.jitbase.com/blog/quality-management-system-examples-cnc-machine-shops) Read more [![Deux techniciens CNC analysant des documents de production devant des machines-outils — calcul du ROI d'un logiciel de gestion de production SaaS - 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[Privacy Policy](https://www.jitbase.com/privacy-policy) ```json { "@context" : "https://schema.org", "@type" : "BlogPosting", "author" : { "@type" : "Person", "name" : "Judicael Deguenon", "url" : "https://www.jitbase.com/blog/author/judicael-deguenon" }, "dateModified" : "2026-11-06T16:13:35.141Z", "datePublished" : "2026-11-06T16:01:43.000Z", "headline" : "First Pass Yield in CNC Shops: FPY Formula and Fixes", "image" : [ "https://www.jitbase.com/hubfs/first-pass-yield-fpy-cnc-shops.webp" ], "mainEntityOfPage" : { "@id" : "https://www.jitbase.com/blog/first-pass-yield-fpy-cnc-shops", "@type" : "WebPage" }, "publisher" : { "@type" : "Organization", "logo" : { "@type" : "ImageObject", "url" : "https://www.jitbase.com/hubfs/logo%20jitbase%201.svg" }, "name" : "JITbase" } } ``` ```json { "@context" : "https://schema.org", "@type" : "FAQPage", "mainEntity" : [ { "@type" : "Question", "acceptedAnswer" : { "@type" : "Answer", "text" : "First pass yield is the share of parts that come out of an operation right the first time, with no rework and no scrap. It is also called first time right. A part that was fixed after inspection may still ship, but it does not count as good in first pass yield. The metric shows the quality of the process itself, not only the quality of what ships. In a CNC shop it reveals the time spent reworking and re-inspecting parts, which scrap rate and final yield do not show." }, "name" : "What is first pass yield?" }, { "@type" : "Question", "acceptedAnswer" : { "@type" : "Answer", "text" : "Take the units that entered the operation, subtract the units that were not right the first time, then divide by the units that entered. For example, if 200 parts are started and 12 are non-conforming, first pass yield is 188 divided by 200, or 94%. The units that were not right include both scrapped parts and reworked parts. If you only subtract scrap, you get final yield instead, and the result will look better than the process really is." }, "name" : "How do you calculate first pass yield?" }, { "@type" : "Question", "acceptedAnswer" : { "@type" : "Answer", "text" : "Final yield counts the parts that are good at the end, including parts that were reworked. First pass yield only counts the parts that were good the first time. In the example of 200 parts with 8 reworked and 4 scrapped, final yield is 98% while first pass yield is 94%. The gap between the two is the rework load. A shop with a high final yield and a much lower first pass yield is shipping good parts. It is paying for them with extra machine time, handling and inspection." }, "name" : "What is the difference between first pass yield and final yield?" }, { "@type" : "Question", "acceptedAnswer" : { "@type" : "Answer", "text" : "No. A reworked part was not right the first time, so it counts against first pass yield, even if it ships after the repair. This is the main difference between first pass yield and final yield. In practice, this means operators must declare reworked parts as non-conforming, not only scrapped parts. If rework is fixed quietly at the bench and never recorded, first pass yield will look higher than it really is." }, "name" : "Does a reworked part count in first pass yield?" }, { "@type" : "Question", "acceptedAnswer" : { "@type" : "Answer", "text" : "Rolled throughput yield is the first pass yield of a whole route of operations. You calculate it by multiplying the first pass yield of each operation. Three operations at 94%, 97% and 99% give a rolled throughput yield of about 90.3%. It shows how much is lost across the full route, even when each operation looks acceptable on its own. To know where to act, keep the first pass yield of each operation as well." }, "name" : "What is rolled throughput yield?" }, { "@type" : "Question", "acceptedAnswer" : { "@type" : "Answer", "text" : "There is no universal target. The right level depends on the parts, the material, the tolerances and the size of the lots. A shop running repeat jobs will not reach the same number as a shop machining prototypes in hard alloys. The best reference is your own trend by machine, part number and operation. Set a baseline over a few weeks, fix the top causes of non-conforming parts, and check that first pass yield rises and stays stable." }, "name" : "What is a good first pass yield for a CNC shop?" } ] } ```