IntRacer offers a simple, instant way to track interest earned over time—based on your initial setup, with no need to link bank accounts or share personal data. Watch your balance grow in real time with continuous updates throughout the day.

Description of the App

This minimalist calculator app lets users enter a one-time setup including their principal amount, AER% interest rates, and start date. It then calculates interest growth per minute and displays the current balance, total interest gained, and today’s earnings on demand, making it ideal for visualizing how money grows over time. Withdrawing funds temporarily reduces the interest rate to the low interest rate for 30 days, after which the higher rate automatically resumes.

Unlike traditional financial systems where interest and balance updates typically occur monthly or quarterly, this app updates interest growth every minute. This real-time calculation provides immediate insight into how your money accumulates, allowing you to trace your account’s growth dynamically and precisely at any moment, offering greater transparency and control over your finances.

How to Use It

Using this application is simple and intuitive. Upon first launch, you’ll be prompted to enter your initial account details, including the principal amount, high and low annual interest rates, account start date, and preferred currency.

The app continuously calculates interest growth on a per-minute basis, displaying your current balance, total interest earned, and today’s gain in real time. To update your account, use the Deposit or Withdraw buttons to enter transaction amounts and dates. You can also adjust the AER% interest rate along with its effective date—the app will automatically apply the new rate and recalculate your interest and total balance from that point forward.

To view your interest growth visually, tap the chart icon. You can choose to display either the accumulated interest or the total balance. To reset all data and start fresh, tap the trash icon.

Note: Any withdrawal will temporarily reduce your interest rate to the lower rate for 30 days. After this period, the higher rate is automatically reinstated.

This app is designed to work fully offline, keeping your data private and secure at all times. The only exception is when it briefly connects to the internet to fetch live currency exchange rates for accurate conversion of your balance into foreign currencies.

How interest is calculated

This app calculates interest based on the Annual Equivalent Rate (AER%) entered by the user. To provide accurate updates at different time intervals (monthly, daily, hourly, or by the minute), the following method is used:

We define:

• α = AER% / 100 (i.e., the AER expressed as a decimal)

• T = Number of compounding intervals per year

• β = Periodic interest rate = (1 + α)^(1/T) - 1 = AGR% / 100 / T

Each period, the balance is updated as: Balance(i+1) = Balance(i) * β

Below is the exsample of compounding intervals, periods per year, and AGR estimates when AER% = 5.

This method ensures that:

• Your interest updates match the compound growth implied by the AER.

• The balance reflects real-time compounding, not just annual totals.

• Accuracy is preserved whether you're viewing changes monthly or minute-by-minute.

Interest Calculation Flow: High/Low Rate Transitions and Withdrawal Impact

1. Daily Compounding:
   Interest is compounded at the end of each day, based on the current balance and the applicable interest rate.
   
2. High Rate Period:
   The account earns a high rate (a) under normal conditions.
   
3. Withdrawal and Penalty (b):
   When a withdrawal occurs, the balance is immediately reduced on that day.
   From that same day onward, the low (penalty) rate (b) is applied to the post-withdrawal balance.
   
4. Penalty Duration:
   The penalty rate continues for a defined period or until criteria are met (e.g. no further withdrawals).
   After this, the high rate (a) resumes.
5. Rate Change (a′):
   A new high rate (a′) can be scheduled.
   The new rate becomes effective on a specific day — it is used at the end of that day to calculate interest into the next day.

Calculation flow is shown below.

Security

This app is built with your privacy and safety in mind from the ground up. It operates entirely offline by default, meaning nothing you enter is transmitted or shared. You will never be asked to provide personal details such as your name, bank account number, or login credentials. The app functions purely as a standalone financial calculator.

All information you enter—including the principal amount, interest rates, start date, and any adjustments—is stored locally on your device using Apple’s secure @AppStorage system. This method ensures your data remains within the app’s sandboxed environment, inaccessible to other apps or systems on your phone.

The only exception to offline operation occurs when the app briefly connects to the internet to retrieve live currency exchange rates. This is used solely to provide accurate foreign currency conversions and does not involve sending any of your data.

If you ever wish to remove your data, a built-in reset option allows you to permanently delete all stored values, instantly returning the app to its original state with no residual information left behind.

Because the app never collects personal data and communicates with external servers only for non-identifying exchange rate retrieval, you can use it with confidence—knowing your information stays private, secure, and fully under your control. It adheres strictly to Apple’s privacy standards for on-device applications.