The Calculator page is the primary entry point for Airgead. It accepts four inputs and shows a live animated balance while you type — no submit button is required to see the preview. Every keystroke immediately recalculates the projection and smoothly animates the displayed balance, so you can explore different scenarios in real time.Documentation Index
Fetch the complete documentation index at: https://mintlify.com/apursley2012/airgead-investment-calculator/llms.txt
Use this file to discover all available pages before exploring further.
The Four Inputs
Each field maps directly to a variable in the compound interest formula. All four fields are required and pre-filled with sensible defaults so you can see a meaningful result as soon as the page loads.The initial investment amount at time zero, in dollars. This is the lump sum you are placing into the investment before any monthly contributions begin. Accepts whole dollar amounts; the step size is $100. Minimum value is 0.
The fixed dollar amount added to the investment at the end of every month throughout the entire projection period. Set this to 0 to model a one-time lump-sum investment with no ongoing contributions. The step size is $25. Minimum value is 0.
The estimated annual interest rate expressed as a percentage (e.g. enter
7 for 7%). The calculator converts this to a monthly rate internally by dividing by 12. The step size is 0.1 percentage points. Minimum value is 0.The projection period in whole years. The calculation runs month by month for the full number of years entered, then presents an annual summary. Minimum value is 1; maximum is 80.
Input Validation
Negative values for any field are automatically clamped to zero. The years value is rounded to the nearest whole number and capped at a maximum of 80. These rules are enforced in
js/lib/calculator.js inside the calculateCompoundInterest() function before any arithmetic is performed, so the preview always reflects a valid calculation even if you type an out-of-range value.Live Preview
As you change any field, three values update instantly below the form without requiring a page submission:- With monthly deposits — the large animated figure at the top of the page. This is the projected final balance after compounding the starting balance and all monthly deposits for the full number of years at the given rate. The number animates with a smooth ease-out curve over 650 ms whenever it changes.
- Without deposits — a quick-stat showing what the starting balance alone would grow to over the same period and at the same rate, with no ongoing contributions.
- Difference — a quick-stat showing how much more the deposit scenario produces compared to the no-deposit scenario (displayed with a
+prefix).
The Notice Line
Directly below the quick stats, a notice line reads:“You earn $X more by contributing monthly.”This line updates automatically alongside the live preview. The dollar amount it cites matches the Difference quick-stat exactly.
Viewing Detailed Results
Once you are satisfied with your inputs, click View Details to proceed to the full Results page.Calculation is saved
The current inputs and the full year-by-year results array are serialized to JSON and written to
localStorage under the key airgead_current_calc.Default Values
The form loads with the following pre-filled defaults so you can see a representative projection immediately:| Field | Default value |
|---|---|
| Starting balance | $5,000 |
| Monthly deposit | $250 / month |
| Annual rate | 5% |
| Years | 20 years |