Let's begin with the top-up screen
Input field
Quick amount button
Top-up method
Current balance
Top-up money type
Other top-up related features
Confirm Button
What do we know about the users through data?
We found that users tend to top up small amounts multiple times instead of adding a larger amount at once.
Why is this a problem?
Each top-up comes with a processing fee—ranging from about ¥10 to ¥200 depending on the method. With PayPay’s large volume of transactions, these fees quickly add up on the operations side.
How do we going to solve it?
So our goal was to reduce the frequency of top-ups and encourage users to add larger amounts per top-ups.
So for this test, we started with the assumption that...
Showing users their total spending from the previous month during the top-up flow could encourage them to add a similar—or at least larger—amount.
Then I broke the assumption down into two key design points:
Show users how much they spent last month
Make it easy to top up that amount with just a tap
This would help users to maintain a sufficient balance throughout the month, reducing the need for frequent top-ups by subtly shifting their behavior.
And I started to generate some potential concepts for testing.
For the first idea, I thought about adding an entry point to the spending history page, making it easy for users to see their past spending.
⚠️ But the problem is, it adds an extra step—users have to leave the top-up flow, check their spending, then navigate back. It interrupts the experience and makes the process feel less seamless.
Next, we needed to make it easier for users to enter that amount.
So I placed the spending amount directly on the top-up page.
So I introduced a new pattern that lets users tap the placeholder to auto-fill the recommended amount.
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For the second option, I considered adding a new quick amount button that displays the spending amount, placed ahead of the other quick amount buttons.
⚠️ But it didn’t sit well visually—it made the layout look off.
So I kept the number but moved the descriptive text into a tooltip for a cleaner layout.
As third idea, I considered adding the button and spending information to the bottom bar.
⚠️ But it made bottom bar too large and could potentially cover content at the bottom.
So I switched to a floating button to make it less intrusive, and added a dismiss icon so users could easily close it.
Let’s take a pause and take a look at our three candidates.
Testing case ①
Testing case ②
Testing case ③
Just when things seemed to be going smoothly, an issue came up— I revisited Testing case 1.
Where I introduced a new pattern that lets users tap the placeholder to auto-fill the recommended amount.
⚠️ Second thought: this felt too aggressive—some users may prefer to enter the amount manually, but when they tapped the placeholder, we automatically filled in a value, which could lead to a poor experience over time.
→
So, I removed the behavior, moved the banner below the input field, and integrated the suggested amount button directly into it.
This made the design less intrusive and kept the input field as the primary focus in the information hierarchy.
Before
After
But thinking one step further—
While we’re making it easier for users to input the amount, what if they tap it by accident?
If they didn’t mean to top up that amount, they’d have to hit the delete key multiple times, which could lead to frustration.
So (drumroll...) I proposed adding a “clear amount” icon button that appears when the input field is focused, which is a common pattern in finance apps.
It’s a small touch, but I believe it also improves the experience for regular users.
And (light bulb moment 💡)—I recalled a research study I conducted with a user researcher on top-up behavior. One key insight was that users avoid keeping large balances in PayPay due to security concerns. As a result, they prefer topping up small amounts more frequently.
Digging deeper, I found that PayPay actually offers a compensation program and several other security measures. The problem, however, is that this information is far too hidden from users.
So I added a security message and a link to the help page to reassure users and boost their sense of safety.
Since I was already working on it, I started thinking—what else can we do to ease users’ concerns?
After a few walks (and maybe a bit of overthinking), an idea came to mind—
Highlight to users that they can cash out anytime, plus a link to the help page.
I chose not to redirect them to the cash-out flow, since they’re in the middle of topping up—and we didn’t want to interrupt that process.
For a final touch, we said we were ready to test… yeah, right.
We knew we wanted to recommend a top-up amount based on users' spending from the previous month. But there were still a few open questions:
When should we show it? How often? And what amount should we recommend?
⏱ Timing Matters
If users see the recommendation in the middle of the month, chances are they’ve already topped up a small amount. At that point, they’re less likely to follow our suggested amount.
To validate this, I reached out to a data team to check the average top-up frequency. The data showed that most users top up about every two weeks, meaning they visit the top-up page roughly twice a month.
👉 So instead of displaying the suggested amount throughout the month, I decided to:
Show it at the beginning of the month, when they’re more likely to make a larger top-up
Limit it to bi-weekly display — shown once every two weeks, and then hide it until the next month. This helps avoid banner fatigue and keeps the suggestion relevant.
📉 What About One-Off Large Expenses?
During QA, I noticed a few users had big spikes in spending—for example, investment-related payments or rare purchases. These aren’t regular behaviors and could throw off the recommended amount.
To keep things accurate, we excluded certain categories from the calculation if they’re clearly not part of regular monthly expenses.
🔢 Round It Up — for Tech and Business Reasons
Lastly, I looked at the actual numbers. Users’ monthly spending often ends in awkward figures—like 14,563. Recommending that exact amount didn’t feel helpful or practical.
From both a technical and business point of view, I decided to round up to the nearest thousand. So if a user spent 14,563 last month, they’d see a suggested top-up of 15,000. It’s cleaner, easier to act on, and nudges the user slightly toward a higher amount.
When we were finally ready to move forward, our data analyst brought up another important point:
If we wanted to test all three options, it would take significantly more time and a larger sample size.
Since our goal was to move fast and iterate, we decided to start with just two options for the initial test. This let us gather insights quickly without slowing down the release.
After some consideration, we decided to drop the floating button option.
It was overlapping content at the bottom of the screen, potentially affecting the visibility of other teams’ feature entry points at the first glance.
👋 Bye Bye
Sometimes in product development, you have to negotiate and make trade-offs.
This idea didn’t make it through—but hey, that’s just part of the process.
Time to reveal the finalists—with a few small updates!
Player ①
I added an extra quick amount button to make it easier for users to input the recommended amount.
To show last month’s spending, I used the input field’s placeholder—since tooltips aren’t ideal for longer text and can impact readability.
Player ②
In this version,
I used a banner to display the user’s spending from the previous month, along with a text button that lets them input the recommended amount with a single tap.
⏩ One month later… we have a winner!
🎉 It’s Player ①
📊 Results
Top-up amount increased
4%
while Player ② showed no significant change.
However, top-up frequency remained unchanged in both groups.
💡 What We Learned from Testing
Showing users their last month’s spending can encourage them to top up more.
Adding a banner is visually prominent, but ironically, it was often overlooked (confirmed by CTR data )
Integrating into the existing layout—such as using a quick amount button—made it more likely for users to notice and take action.
The clear amount icon button received positive feedback for making it easy to delete input.
These learnings reminded us that it’s an iterative process, and I also shared them with the design team members.
Reflection
I learned that having a clear reason behind each deisign decision really matters. Even if things don’t work out, understanding the thinking behind it helps you grow and avoid repeating mistakes.
I also found that past research can be surprisingly helpful—it often supports new ideas in ways you wouldn’t expect.
Next ➞
Sign-up flow revamping
2025/2 - 2025/6
End-to-end design process
PayPay
Since joining PayPay, I’ve been responsible for improving the top-up experience, with a focus on understanding user concerns when adding funds.
In this project, we ran an A/B test to explore which UI pattern best encourages users to top up larger amounts. which can increase their spending, and reduce top-up frequency—ultimately helping to lower operational costs. Over a one-month period, we tested two different UI patterns.
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Copyright © 2025 by Ryan Chang