How Do WeChat & Alipay Process Billions Daily? Inside Their Settlement System Design

Settlement Business Overview

Payments follow a three‑stage model: transaction, clearing, and settlement. Transaction records user payment actions; clearing aggregates and calculates amounts; settlement transfers funds based on clearing results.

Three‑Party Settlement Modes

T1: next business day settlement after same‑day transaction.

D1: next calendar day settlement, available 365 days.

D0: same‑day settlement, available 365 days.

H0: hourly settlement at fixed times (e.g., 9:00, 10:00).

S0: per‑transaction settlement, either automatic or merchant‑initiated.

TD: cross‑day settlement for merchants with peak activity around midnight.

Settlement Account Models

Three primary designs are used:

Intermediate Account Model – a “merchant pending settlement” account holds funds after a successful transaction; during settlement the amount moves to the merchant settlement account (or directly to a card).

Freeze Model – the merchant settlement account is split into “frozen balance” and “available balance”; settlement unfreezes funds into the available balance.

Bill Model – no intermediate settlement account; a “merchant receipt account” is used for balance verification, and settlement bills are generated directly from clearing details.

Intermediate accounts are optional depending on the chosen model; freeze and bill models do not require them.

Settlement Directions

Funds can be settled to a bank card (direct transfer to the merchant’s signed account) or to a virtual account on the platform, from which merchants can later withdraw.

Settlement Triggers

Automatic settlement follows predefined agreements and schedules, while self‑service settlement requires merchants to submit settlement requests within the allowed cycle.

Key Settlement Metrics

From the provider perspective: accuracy, security, user satisfaction, and low complaint rates. From the merchant perspective: bank coverage, service quality, fast arrival, and low cost.

System Architecture

Core components include:

Scheduled‑task manager to drive settlement cycles.

Merchant backend for merchants to initiate and query settlements.

Operations backend for internal staff.

Accounting system supplying settlement data and receiving payout notifications.

Advance‑fund system handling D0/S0 advance requests.

Billing system calculating fees (e.g., ¥2 per transaction).

Merchant system providing merchant‑related information.

The architecture diagram (see image) illustrates these interactions.

Settlement Processing Flow

The end‑to‑end flow consists of data preparation, core settlement processing, payout handling, and result updates.

Data Preparation

The account system generates files of eligible transactions and pushes them to the settlement system for parsing.

Core Settlement Processing

Eligible transaction data are aggregated into settlement statements. Different processing types include T1, D1, and self‑service settlements, each with its own workflow diagram.

Payout Handling

After settlement, payout requests are created. For D0‑type products, an advance‑fund request is made before the payout. The payout result updates the payout status.

Data Relationships

Various documents are produced: transaction data → pending settlement → settlement statements → payout requests, forming a linked chain (see diagram).

Backend Prototypes

Key UI screens demonstrate:

Settlement information management – merchant contracts, settlement modes, cards, last settlement date.

Settlement rule management – configurable rules per business or default rules.

Pending settlement data – incoming transaction data awaiting settlement.

Settlement records – successful and failed settlement logs, with reasons such as negative net amount or unmet minimum thresholds.

These screens provide a visual overview of the settlement system’s functionality.