Bonus Tolerance Calculator
This bonus has nothing to do with pay. In GD&T, bonus tolerance is the extra geometric tolerance a feature earns when its actual size departs from its material condition, and it is often the difference between a part that passes inspection and a part that gets scrapped. This bonus tolerance calculator takes the feature type, its size limits, the specified geometric tolerance and the measured size, and returns the bonus, the total allowable tolerance, the MMC and LMC sizes, the virtual condition, and a straight pass-or-fail check on size.
It covers the cases the true-position-only tools leave out: holes, pins, slots, tabs and bosses; MMC, LMC and RFS modifiers; and six tolerance types, position, perpendicularity, parallelism, angularity, concentricity and symmetry. The modifier decides whether a bonus exists at all, so the calculator makes you state it rather than assuming MMC.
GD&T planning aid. Bonus applies per feature; verify final acceptance against the drawing and your quality standard.
Quick Answer
Key takeaways
- Bonus is departure, nothing more exotic: how far the actual size sits from the material condition size. A hole at its smallest (MMC) earns zero; every step toward LMC adds the same amount to the geometric tolerance.
- The bonus can never exceed the size tolerance range, here 0.20 mm. A feature outside its size limits earns nothing and fails on size, however well placed it is.
- RFS earns no bonus, ever. If the feature control frame has no M or L modifier, the stated tolerance is the whole tolerance.
- Virtual condition, not the bonus, is the number the mating part is designed around: 9.700 mm here, the smallest effective boundary the hole can present.
- Quick Answer
- How to read a drawing into this calculator
- The bonus formulas, by feature and modifier
- Worked example: a 10 mm hole, position at MMC
- MMC, LMC and RFS side by side
- Virtual condition: the boundary the mating part sees
- What competing calculators miss
- Frequently Asked Questions
- Add This Calculator to Your Website
- References
How to read a drawing into this calculator
You need five things from the drawing and one from the part: the feature, the modifier, the size limits, the stated tolerance, and the measured size.
Start with the feature control frame. Its symbol gives the tolerance type, its number gives the specified tolerance, and a circled M or L after that number gives the material condition. No circle means RFS. The size dimension gives the nominal and its plus and minus limits. Then measure the feature: the actual size is what turns a stated tolerance into a total allowable one. Enter all of it, keeping every value in one unit, and the result adds the departure note, the size verdict and the virtual condition that a bare bonus figure leaves you to work out yourself.
One habit prevents most errors: enter the minus tolerance as a positive number. The drawing prints 10 ± 0.10, or 10 +0.10/-0.10; both fields here want 0.10. Entering -0.10 in the minus field is rejected, because a negative limit would silently flip which end of the range is MMC.
The bonus formulas, by feature and modifier
Internal and external features read the size limits in opposite directions, because maximum material means opposite ends of the range for a hole and for a pin.
Find the material condition sizes. Internal feature (hole, slot): MMC = nominal – minus tolerance (smallest size, most material around it); LMC = nominal + plus tolerance. External feature (pin, tab, boss): MMC = nominal + plus tolerance (largest size); LMC = nominal – minus tolerance.
Measure the departure. At MMC: bonus = |actual size – MMC size|. At LMC: bonus = |actual size – LMC size|. At RFS: bonus = 0, by definition.
Add it to the stated tolerance. Total allowable tolerance = specified geometric tolerance + bonus. This total is the zone your measured geometric error is compared against.
Check size separately. If the actual size is outside the limits, stop: the feature fails on size and the bonus is zero for acceptance, whatever step 2 produced.
The concepts follow the material condition rules in ASME Y14.5, the dimensioning and tolerancing standard the M and L modifiers come from. As the trade coverage of the standard’s approach puts it, bonus exists because a feature that departs from its worst-case material boundary leaves clearance behind, and GD&T lets the geometric tolerance spend that clearance instead of wasting it. The worked example in Machine Design’s bonus tolerance walkthrough runs the same departure arithmetic on a flange hole: actual size minus MMC size, added to the stated position tolerance.
Worked example: a 10 mm hole, position at MMC
The calculator is pre-filled with this case, a standard teaching example: hole, nominal 10 mm, ± 0.10, position tolerance 0.20 at MMC, measured at 10.05 mm.
| Figure | Value |
|---|---|
| MMC size (10 – 0.10, smallest hole) | 9.900 mm |
| LMC size (10 + 0.10, largest hole) | 10.100 mm |
| Departure from MMC (|10.05 – 9.90|) | 0.150 mm bonus |
| Total allowable (0.20 + 0.15) | 0.350 mm |
| Tolerance increase from bonus | 75.0% |
| Size within limits (9.900 to 10.100) | Yes |
| Virtual condition (9.90 – 0.20) | 9.700 mm |
Watch the bonus grow across the size range and the pattern becomes obvious: it is a straight line from zero at MMC to the full size range at LMC.
| Actual hole size | Bonus | Total allowable position |
|---|---|---|
| 9.90 mm (at MMC) | 0.000 mm | 0.200 mm |
| 9.95 mm | 0.050 mm | 0.250 mm |
| 10.00 mm | 0.100 mm | 0.300 mm |
| 10.05 mm (worked example) | 0.150 mm | 0.350 mm |
| 10.10 mm (at LMC) | 0.200 mm | 0.400 mm |
MMC, LMC and RFS side by side
The three modifiers answer three different design worries, which is why the same feature can carry any of them. Picking the wrong one in the calculator reverses the bonus direction.
MMC (M)
Protects assembly fit. Bonus grows as the feature departs from its maximum material size: a bigger hole, a smaller pin. The common case for bolted joints and anything checked with a functional gauge.
LMC (L)
Protects what is left behind: wall thickness, edge distance, minimum material. Bonus grows as the feature departs from its least material size, in the opposite direction from MMC.
RFS (no modifier)
Protects location or orientation for its own sake, regardless of size. No bonus at any size. The stated tolerance is the whole tolerance, and size cannot rescue a badly placed feature.
The LMC direction is worth one worked check, because it is the case people most often run backwards. Take the same 10 ± 0.10 mm size limits on a pin instead of a hole, position 0.20 at LMC, measured at 9.95 mm. For the pin, MMC is 10.100 mm (largest) and LMC is 9.900 mm (smallest). Departure from LMC is |9.95 – 9.90| = 0.050 mm of bonus, total allowable 0.250 mm, and the LMC boundary (formally the resultant condition) is 9.900 – 0.20 = 9.700 mm. Enter pin, LMC and 9.95 in the calculator and those are its exact outputs. The fuller treatment in CMM Quarterly’s bonus tolerance guide makes the same point from the inspection side: no M or L in the frame, no bonus, whatever the size.
Virtual condition: the boundary the mating part sees
Virtual condition is the worst-case boundary the feature can present to whatever mates with it: for the worked-example hole, 9.700 mm, the smallest effective opening once position error is spent.
Design and inspection both key off this number. A mating pin, or a functional gauge pin, sized at the virtual condition must always pass, because the hole can never effectively be smaller than its virtual condition while it conforms. That is why a drawing can allow a generous 0.35 mm of position error on a real part and still guarantee assembly: the guarantee lives at the boundary, not in any single measurement. At LMC the matching boundary is formally called the resultant condition, and the calculator labels it that way in the result rather than borrowing the MMC term.
What competing calculators miss
The tools that rank for GD&T bonus work are true-position calculators, and position is only one of the six characteristics that take these modifiers.
Miss 1: position only, one feature assumed. The GD&T Basics and CalcExp true-position tools compute a position bonus for a generic round feature. Perpendicularity, parallelism, angularity, concentricity and symmetry callouts, and slots, tabs and bosses as distinct internal or external features, are outside their frame. This calculator spans all six types and all five feature types, with the internal/external direction handled by the feature choice rather than left to the reader.
Miss 2: no LMC. Position tools are built around MMC, because assembly is the common story. LMC callouts exist to protect wall thickness, and their bonus runs the other way; a tool that only knows MMC will compute an LMC part backwards and pass or fail it wrongly. The pin example above is the check: 0.050 mm of bonus at LMC, against the 0.150 mm an MMC reading of the same measured size would invent.
Miss 3: the answer stops at the bonus. A bonus figure alone does not accept a part. You still need the size verdict (outside the limits means fail, bonus or not), the virtual condition for the mating part or gauge, and, for a pattern, the reminder that each feature earns its own bonus. This calculator reports all of them in the same result, which is the difference between a number and an inspection decision.
Frequently Asked Questions
Bonus tolerance is the additional geometric tolerance that becomes available when a feature of size departs from its material condition, MMC or LMC. The departure amount is added to the stated tolerance. A hole made exactly at its MMC size earns no bonus; in the worked example, a hole 0.15 mm away from MMC earns 0.150 mm.
Maximum Material Condition is the size at which the feature contains the most material. For a hole it is the smallest diameter (10 – 0.10 = 9.900 mm in the worked example); for a pin or shaft it is the largest diameter. Bonus tolerance is most commonly used with the MMC modifier, shown as a circled M in the feature control frame.
MMC allows bonus tolerance as the feature departs from its maximum material size, which protects assembly fit. LMC allows bonus as the feature departs from its least material size, which protects wall thickness and edge distance. RFS, regardless of feature size, gives no bonus at all: the geometric tolerance applies in full at any size.
No. The bonus is capped by the total size tolerance range, LMC minus MMC, which is 0.200 mm in the worked example. A feature made at the far limit earns that full range as bonus and no more, and a feature outside its size limits fails on size regardless of any bonus.
Virtual condition is the worst-case boundary generated by the material condition size combined with the geometric tolerance: MMC minus the tolerance for an internal feature, MMC plus the tolerance for an external one. The worked-example hole has a virtual condition of 9.700 mm. Mating parts and functional gauges are designed around this boundary so the assembly always fits.
Yes, individually. In a bolt-hole pattern, each hole earns a bonus from its own measured size, so two holes in the same pattern can legitimately have different total allowable tolerances. Set the feature count above 1 and the result notes this; composite tolerancing can then control the pattern as a group on top of the individual bonuses.
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References
- Machine Design, “Ensuring Parts Fit, Using Bonus Tolerance to Your Advantage”: the departure formula, functional gauging at virtual condition, and the scrap and throughput benefits of bonus tolerance. Machine Design: Bonus Tolerance to Your Advantage. Accessed October 2026.
- CMM Quarterly, “Ensuring Parts Fit, Using Bonus Tolerance to Your Advantage”: the inspection-side treatment, including the rule that no M or L modifier in the feature control frame means no bonus. CMM Quarterly: Bonus Tolerance Guide. Accessed October 2026.
- FARO, “GD&T for beginners: MMC and bonus tolerance, explained in 3D”: pin examples at MMC, at LMC and between them, showing how the bonus grows with departure. FARO: MMC and Bonus Tolerance Explained. Accessed October 2026.
- CNC Lathing, “GD&T MMC: Definition, Formula, Calculation, Bonus Tolerance, Uses”: MMC and virtual condition formulas for internal and external features. CNC Lathing: GD&T MMC Guide. Accessed October 2026.
- CNC Guides, “GD&T MMC Definition, Formulas, Design and Uses”: virtual condition boundaries for holes and pins, and how MMC protects assembly clearance. CNC Guides: GD&T MMC Definition and Formulas. Accessed October 2026.