Quality
How to Chart First Pass Yield Month Over Month in Excel
A monthly first pass yield line looks reassuring precisely because averaging is a form of hiding. Here is how to build the chart properly, and the multiplication that turns four good stations into a mediocre line.
Charting first pass yield month over month is a request that sounds like a formatting question and is really a measurement question. The chart is easy. The problem is that a monthly average of a daily metric smooths away exactly the variation you need to see, and a line that drifts between 94% and 96% for a year can contain individual weeks in the seventies that nobody ever looked at. Build the chart so the variation survives.
Get the data shape right first
You need one row per production period per line, with three columns: units started, units passing first time, and the period date as a real Excel date rather than text. First pass yield is the ratio, computed in the sheet. Do not store the percentage as an entered value, because then you cannot re-aggregate: a monthly figure has to be total passed over total started for the month, not the average of the daily percentages. Those two produce different answers whenever daily volume varies, and the average-of-averages version is the wrong one.
Build the chart in three moves
The build
- Pivot the raw rows to month, summing units started and units passed, then compute yield in a calculated column so the aggregation stays correct.
- Insert a line chart on the monthly yield, then add the daily or weekly yield as a light scatter behind it so the spread inside each month stays visible.
- Fix the vertical axis to a range that reflects your process, not zero to one hundred. An axis starting at zero flattens every real move into a straight line near the top.
The trap: your line yield is not your station yield
Rolled throughput yield is the product of the station yields, not their average, and the difference is brutal. 4 stations each running a respectable 97% multiply to about 88.5% at the end of the line. Every station manager can report a good number while the line delivers a mediocre one, and nobody in that meeting is lying. If your chart shows line-level yield only, add a small multiples panel with one sparkline per station, because the line number will never tell you which station moved.
- Yield at each of four stations: 97%
- Rolled throughput yield of the line: 88.5%
- Loss the station numbers hide: 11.5%
Four stations at ninety-seven percent do not make a line at ninety-seven percent. Yields multiply, and the meeting where everyone reports a good number is exactly where that gets forgotten.
What to do with the chart once it exists
A yield chart earns its keep only if a move on it triggers something. Set a control limit from your own historical variation rather than a round target, mark it on the chart, and agree in advance what happens when a month breaches it. Without that, the chart becomes a monthly ritual that documents decline without interrupting it, which is the most common fate of every quality metric that gets plotted and never acted on.
Use the first pass yield calculator to verify line and station figures before charting them. Check your yield math
Published 2026-08-08.