The three accepted bases for maximum allowable carryover — and how to turn a MACO into swab and rinse limits.
Maximum allowable carryover — MACO — is the single number a cleaning validation programme is built to defend: the most residue from one product that may be carried into the next batch without putting a patient at risk. Get it right and every swab limit, rinse limit, and acceptance criterion downstream follows from it. Get it wrong, or calculate it in an unvalidated spreadsheet, and the error propagates silently through the whole programme until an inspector finds it.
The calculation itself is not complicated. What trips teams up is that there are three accepted ways to arrive at a MACO, they can give very different numbers, and the basis you choose has to be scientifically justified rather than convenient. This page walks through all three, works a full example, and gives you an interactive calculator to run your own numbers.
A MACO is only as defensible as the basis behind it. The most conservative scientifically justified value is the one that governs — not the one that is easiest to pass.
Regulators and industry guides recognise three ways to set a carryover limit. Current expectations — EU GMP Annex 15, the EMA HBEL guideline, and the APIC guide — favour the health-based method; the dose-based and 10 ppm approaches remain in use as the legacy criteria and as quick baselines.
MACO = (ADE_previous × MBS_next) / MDD_nextADE_previous = acceptable daily exposure of the product being cleaned away (mg/day); MBS_next = minimum batch size of the next product; MDD_next = maximum daily dose of the next product (mg/day). This is the method EU GMP Annex 15, the EMA HBEL guideline, and the APIC guide prefer, because it is anchored in toxicological data specific to the molecule.
MACO = (TDD_previous × MBS_next) / (SF × TDD_next)TDD = therapeutic daily dose; SF = safety factor, commonly 1000 for oral products and higher for injectables. The historical criterion of 0.1% of the therapeutic dose corresponds to a safety factor of 1000.
MACO = 10 mg/kg × MBS_nextCaps residue at 10 parts per million of the next batch. A useful baseline where health-based data is unavailable, often combined with another method and the lowest resulting value applied.
ADE and PDE are used interchangeably in practice — both name the daily exposure considered safe over a lifetime, and HBEL (health-based exposure limit) is the umbrella term the EMA guideline uses for them. The safety factor in the dose-based method plays the equivalent role, building margin below the therapeutic dose. Each basis is grounded in a published source: EU GMP Annex 15 (2015) requires carryover limits based on a toxicological evaluation; PIC/S PI 006-3 sets out the legacy carryover triad; the APIC cleaning validation guide gives the health-based MACO formula; and the FDA 1993 Guide to Inspections — Validation of Cleaning Processes remains the foundational US reference, though it deliberately sets no fixed numeric limit.
Total MACO is the carryover allowed across the whole shared equipment train. To use it on the floor, it is converted into sampling limits. The swab limit is the MACO divided by the total shared surface area, multiplied by the area actually swabbed — swab limit = MACO ÷ total shared surface area × swabbed area. The rinse limit is the MACO divided by the total final rinse volume — rinse limit = MACO ÷ total final rinse volume. The calculator below performs both conversions once you have a MACO.
The dose-based method is the clearest illustration because it shows the safety factor doing its work.
Take a previous product with a therapeutic daily dose of 250 mg/day, and a next product with a therapeutic daily dose of 500 mg/day and a minimum batch size of 50 kg. Apply a safety factor of 1000, typical for oral products. Converting the batch size to milligrams (50 kg = 50,000,000 mg):
MACO = (250 × 50,000,000) / (1000 × 500) = 25,000 mg = 25 g
So up to 25 g of the previous product may be carried across the shared equipment train into the next batch. That ceiling is what every swab and rinse limit must then sit beneath — and it is the number an inspector will ask you to justify.
Run your own numbers below. Pick the method, enter the inputs it needs, and the MACO updates instantly, with optional swab and rinse limits as a second step.
Pick a method, enter the inputs it needs, and get the maximum allowable carryover. Everything computes in your browser — nothing is sent anywhere.
These are the acceptance targets derived directly from the MACO — the residue before any analytical recovery factor is applied. See the swab sampling procedure for how recovery adjusts the limit the lab tests against.
CLEEN computes MACO automatically across your whole product matrix — every product pair, every basis, kept current as the mix changes. See how CLEEN automates cleaning validation.
The methodology does not change as a facility grows; keeping every MACO current does. A programme run in spreadsheets captures a moment in time, while the product mix and equipment keep moving underneath it.
Each product-pair MACO is worked out by hand or in an unvalidated spreadsheet, where a single transposed batch size or surface area carries an error through every downstream limit unnoticed.
MACO is computed for every product pair across the train, applying each basis and taking the most conservative value automatically, with the calculation validated and fully traceable.
The basis is chosen once and rarely revisited, so a limit can sit on a legacy 10 ppm number long after the programme has moved to health-based limits.
All three bases are computed in parallel and the most conservative scientifically justified value governs by rule, applied consistently across the whole matrix.
A new product means re-running the calculations by hand, and the worst-case is re-evaluated only when someone remembers to.
A new product entering the master list re-evaluates the worst-case and recalculates affected MACOs automatically, so the limits reflect the live product mix.
Surface areas and rinse volumes are looked up and limits derived by hand per piece of equipment — a slow, error-prone step.
Swab and rinse limits are derived from the MACO and current equipment geometry in one step, ready to drop into the sampling plan.
One multi-site manufacturer cut cleaning validation cycle times by 80 percent across seven facilities while eliminating manual calculation errors — you can see how a multi-site manufacturer scaled cleaning validation across 7+ facilities. A modern cleaning validation software approach keeps MACO limits, the worst-case matrix, and protocols tied to the current product list. For the wider context, see the step-by-step cleaning validation protocol guide and the regulator-by-regulator guidelines.
MACO (maximum allowable carryover) is the maximum quantity of residue from one product that may be carried over into the next product manufactured on shared equipment without posing an unacceptable risk to the patient. It is calculated from the previous product's safety limit (a health-based exposure limit, the therapeutic dose, or a general 10 ppm limit), the next product's batch size and daily dose, and the shared equipment surface area. Every swab and rinse acceptance limit is then derived from the MACO.
Current regulatory expectations (EU GMP Annex 15, the EMA HBEL guideline, APIC) favour the health-based PDE/ADE method because it is grounded in toxicological data specific to the molecule. The dose-based 1/1000th method and the 10 ppm general limit remain in use as legacy criteria and quick baselines. Where more than one applies, the most conservative scientifically justified value governs, so many teams calculate more than one and take the lowest.
The safety factor reflects how much margin you build in below the therapeutic dose. A factor of 1000 is commonly used for oral products; higher factors are applied for more critical routes such as injectables, and for potent or sensitising compounds. The choice should be justified by the route of administration and the toxicity of the compound, not selected to make a limit easier to meet.
Swab sampling targets defined, hardest-to-clean locations — corners, joints, dead legs — and gives a direct surface measurement, so a swab limit is expressed per swabbed area. Rinse sampling assesses large or inaccessible surfaces a swab cannot reach by analysing the final rinse, so a rinse limit is expressed against the total rinse volume. Most programmes use both: the swab for direct hot-spots and the rinse for total and internal surface area.
In practice ADE (acceptable daily exposure) and PDE (permitted daily exposure) are used interchangeably — both express the dose of a substance a person can be exposed to daily over a lifetime without appreciable health risk, derived from the same toxicological logic. HBEL (health-based exposure limit) is the umbrella term the EMA guideline uses for this category. For a MACO calculation you can treat ADE and PDE as the same input.
Cleaning validation software computes MACO across every product pair in the equipment train automatically — applying each accepted basis, taking the most conservative value, and converting it into swab and rinse limits — using the current product list, batch sizes, and surface areas. Because the matrix is data-driven, introducing a new product re-evaluates the worst-case and the limits without manual recalculation, eliminating the transcription errors that unvalidated spreadsheets introduce.
The MACO that survives an inspection is the one whose basis, inputs, and arithmetic a reviewer can follow — and that stayed current as the product mix changed around it.