Simplifying UPI with Inline Calculations

The Everyday Problem

Rahul, a 25-year-old marketing professional, stops by a local tea stall with his colleagues after a long meeting. They order multiple cups of tea, some biscuits, and a few cigarette packs.

As usual, Rahul asks the shopkeeper, “Bhaiya, kitna hua?” (How much is the total?). The shopkeeper, juggling multiple customers, tries to recall the items, does a quick mental calculation, and says, “₹143.”

Rahul, a bit skeptical, pulls out his phone, opens the calculator app, and starts adding up the individual prices. The total comes to ₹135. When he points this out, the shopkeeper realizes his mistake and corrects the total.

Rahul then switches to his UPI app, enters ₹135 manually, and makes the payment. The entire process, which should have been quick, took unnecessary time and effort.

What if Rahul’s payment app had a built-in calculator? Instead of switching apps, he could have tapped a small "Calculator" button within the UPI app, added the prices, and paid instantly—saving time and avoiding errors.

This is the problem we are solving.

Target Users

Currently, users must either:

• Rely on shopkeepers to manually total items (which can lead to errors).

• Manually switch to a calculator app, enter amounts, memorize the total, and then switch back to the payment app—causing friction and delays.

Goal

The goal is to integrate a simple, built-in calculator within payment apps so users can total their purchases without leaving the app, improving speed and accuracy.

My Role & Approach

As a UI/UX designer, I initiated this self-driven case study based on real-world observation. I mapped user pain points, explored comparable design patterns, and created conceptual designs showing how this feature could work across Google Pay, PhonePe, Paytm, and CRED. The goal was to make the feature feel native within each app’s UI.

Constraints & Challenges

• No existing industry precedent: No major UPI or payment app has implemented this feature.

• Balancing simplicity with functionality: The calculator should not clutter the UI or slow down transactions.

• User habit formation: Users are accustomed to external calculators; encouraging adoption of an in-app calculator is a challenge.

Design Concept

The proposed solution adds a calculator icon directly to the UPI payment screen. This icon is placed near the amount field or action button, depending on the app's layout.

When the user taps the icon, a full-screen calculator smoothly replaces the numeric keypad. Users can add item prices, do basic math (e.g., 12 x 4 + 20 x 2 + 10), and the result is automatically shown. Once calculated, the "Pay" button updates with the total amount, making the transition from calculation to payment effortless.

This avoids switching between apps, eliminates mental math, and ensures the correct amount is always paid — especially useful in informal or high-traffic purchase scenarios.

Visual Integration Across Apps

Beyond Google Pay, I explored how this feature could be integrated into other major UPI apps. In PhonePe, a small floating calculator icon sits near the "Send" button, ensuring visibility without disrupting the flow. Paytm places the icon just above the numeric keypad, close to where users input the amount. For CRED, a minimal “Open calculator” text link fits seamlessly beneath the amount field, preserving the app’s clean, premium design.

Outcome & Takeaways

This concept reduces context-switching, minimizes errors, and speeds up UPI payments in informal retail settings. It’s a small addition with a large impact, offering a smoother experience in a space where every second and tap matters. The process reminded me how solving “invisible” friction can significantly improve real-world usability.