The short answer
An aggregated MID is a Visa/Mastercard merchant identification number that aggregates (pools) card transactions from many underlying businesses under a single merchant of record. Stripe has one aggregated MID; every single Stripe customer's transactions flow through it. Same for Square, PayPal, Shopify Payments. The opposite is a dedicated MID — one MID per merchant, each underwritten individually by the acquirer.
Where aggregated MIDs are used
- PayFac model. Payment facilitators by definition use aggregated MIDs. One master MID, many sub-merchants.
- Marketplace model. Stripe Connect, Adyen for Platforms, Braintree Marketplace — all aggregate seller volume under one MID per platform.
- Some ISO-placed accounts. A minority of smaller ISOs aggregate their merchants under one MID at the acquirer to reduce setup overhead; this is considered lower-quality placement and industry guidance is to avoid it.
What operators need to know
- Chargeback ratios are calculated per-MID, not per-sub-merchant. Your own chargeback rate could be 0.3% (well below 1% threshold) but if the aggregated MID's total chargeback ratio crosses chargeback thresholds, the card networks apply pressure to the whole MID, which cascades to you.
- Interchange pricing is blended, not passed through. Because the PayFac negotiates one pricing tier with the acquirer for the entire aggregated MID, you pay flat (2.9% + $0.30) regardless of whether your actual interchange on a given transaction is 0.80%, 1.65%, or 2.40%. Volume operators lose margin to the PayFac here.
- Risk profile is shared. Visa's VAMP program, Mastercard's Excessive Chargeback Merchant (ECM) program, and MATCH listing are all applied at MID level. An aggregated MID carries portfolio-wide risk exposure.
- Funding flows through the aggregator. The acquirer deposits to the PayFac daily; the PayFac then distributes to you per their payout schedule (T+2 to T+7 typical). You do not receive direct acquirer settlement.
- Account-level termination affects all downstream merchants. If the acquirer terminates the master MID (rare but documented — Wirecard collapse, FTX aftermath), every sub-merchant loses processing simultaneously.
Aggregated MID vs. dedicated MID decision
Small operators (under $200k/year): aggregated MID (PayFac) almost always wins on setup friction and speed. Mid-to-large operators ($500k+/year across a portfolio): dedicated MIDs or a parent merchant account with clean soft descriptors win on cost of funds and risk isolation. See our pricing page for the volume-tier decision math. multiflow's parent merchant account model is a hybrid: one parent MID underwritten at an acquirer, with each sub-brand operating under its own soft descriptor — capturing the consolidation benefits of aggregation without the flat pricing or shared risk of a true PayFac aggregated MID.