GD&T Bonus Tolerance Calculator (MMC and LMC)
Bonus tolerance is the extra position or orientation tolerance a feature earns when its size moves away from maximum material condition (MMC). This calculator shows exactly how much bonus a measured hole or pin earns and whether the measured position fits the enlarged zone.
Your numbers
For a hole, MMC is the smallest size. For a pin, MMC is the largest size.
Smallest hole diameter or largest pin diameter allowed by the size tolerance.
Opposite size limit of the same feature.
Local size measured on the part.
The value in the feature control frame before the circle M.
Your results
Follows the ASME Y14.5 and ISO 2692 idea of MMC bonus tolerance. It does not apply to features controlled RFS or to datum features of size with their own shift. Always confirm against the feature control frame on your drawing.
Total position tolerance vs measured feature size (internal feature)
Sweeps Measured actual size from 10 to 10.1, holding your other inputs fixed.
Apply bonus rules to your CMM data
Optional: a short review of how to feed CMM size and position results into your ERP quality records with bonus tolerance applied.
Optional. The tool and every export work without this. No spam.
How to use the calculator
Pick whether the feature is internal (hole, slot) or external (pin, boss). Enter the size limits so the tool knows which size is MMC and which is LMC, then enter the measured actual size and the position tolerance printed in the feature control frame. Add the measured X and Y offsets from the CMM report to test pass or fail. The chart shows how the total zone grows from the stated tolerance at MMC to the maximum at LMC, which is useful when you are deciding how much manufacturing room a size tolerance really gives.
The formula behind bonus tolerance
For an internal feature the bonus equals the actual size minus the MMC size. For an external feature it equals the MMC size minus the actual size. The bonus can never be negative and can never exceed the size tolerance, so it is clamped between zero and the difference between LMC and MMC. The total zone is the stated tolerance plus the bonus. A hole of 10.00 to 10.10 mm with a 0.20 mm position tolerance at MMC and an actual size of 10.06 earns 0.06 mm of bonus and has a 0.26 mm zone.
- MMC for a hole is the smallest allowed diameter
- MMC for a pin is the largest allowed diameter
- Bonus applies only when the M modifier appears after the tolerance
- LMC modifier works the same way but measured from the LMC size
Reading the result and common mistakes
The measured deviation is diametral: twice the radial distance of the feature axis from true position. Comparing a radius to a diameter zone is the most common inspection mistake and passes bad parts. The second mistake is applying bonus to a feature controlled RFS, where the zone stays fixed. For LMC callouts, bonus is earned as the feature approaches MMC, so change the inputs accordingly and treat the LMC size as the reference size. Finally, remember that a pass here covers position only, form and orientation controls on the same feature still apply.
Frequently Asked Questions
What is bonus tolerance in GD&T?
Bonus tolerance is additional geometric tolerance granted when a feature of size departs from its maximum material condition. It only applies when the feature control frame has the MMC (or LMC) modifier. The total allowed zone is the stated tolerance plus the bonus.
Does bonus tolerance apply to profile or flatness?
It can apply to any geometric control on a feature of size when the MMC modifier is used, including position, perpendicularity, parallelism and straightness of an axis. It does not apply to controls on surfaces such as flatness or profile of a surface, which have no size to depart from.
Why is my CMM true position twice my X/Y offset?
True position is reported as a diameter. A feature that is 0.05 mm off in X and 0.08 mm off in Y sits about 0.094 mm from the true point, so the reported true position is about 0.189 mm. Compare that diameter with the diameter zone.
Can bonus tolerance be negative?
No. If the actual size is beyond MMC the part is out of size tolerance and is rejected on size. Within the size limits the bonus runs from zero at MMC up to the full size tolerance at LMC.
If your CMM results live in an ERP quality module such as SAP QM or SyteLine, Netray can help pull measured features into a review that applies bonus rules automatically. This tool works fine without that.
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