The Unified Payments Interface (UPI) is a real-time payment system, built by the National Payments Corporation of India (NPCI), that lets users transfer money between bank accounts instantly using a mobile phone, without sharing account or IFSC details for every transaction.

What Is It (Definition)

Definition: UPI is an instant, mobile-based interbank payment system that links multiple bank accounts to a single mobile application and lets a user pay using a Virtual Payment Address (VPA) instead of account details.
Contrast: Unlike NEFT or RTGS, which are bank-to-bank transfers processed in batches or with manual entry of account details, UPI settles in real time and needs only a VPA or a QR code scan.

How It Works

Virtual Payment Address: Each user links a bank account to a VPA (e.g., name@bank) through a UPI app.
Payment request: The payer initiates a transfer to the payee's VPA or scans a QR code.
NPCI switch: The request routes through NPCI's central switch, which verifies both banks.
Authentication: The payer confirms with a UPI PIN.
Real-time settlement: Funds move between the two bank accounts instantly over the underlying Immediate Payment Service (IMPS) rails.

Key Features

Interoperability: Works across banks and across UPI apps — a user on one app can pay a VPA registered on another.
24x7 availability: Functions every day, including bank holidays.
No account details needed: A transaction needs only a VPA or QR code, not the payee's account number and IFSC code.
Two-factor by design: Every transaction needs the device (registered mobile) and a UPI PIN, combining possession and knowledge factors.

Real-Life Relevance

A street vendor displaying a UPI QR code can receive a payment directly into their bank account within seconds, without needing a card machine or cash handling — this is the single largest driver of UPI's spread into India's informal retail economy.

Significance

Financial inclusion: UPI is a core pillar of India's JAM trinity (Jan Dhan–Aadhaar–Mobile) approach to bringing informal-economy transactions into the formal banking system.
Global benchmark: The International Monetary Fund (IMF) has cited UPI as a model for real-time retail payment systems.
Digital Public Infrastructure export: India has exported the UPI model, or interoperable versions of it, to several countries, including France, Sri Lanka, UAE, Singapore, Mauritius, Bhutan, Nepal and Peru.