> ## Documentation Index
> Fetch the complete documentation index at: https://sdk.grid.is/llms.txt
> Use this file to discover all available pages before exploring further.

> A simple HTTP API to calculate interest rates and years to save up a target amount.

# Goal seek

<Tip>
  More details on our Python examples can be found in our [GitHub
  repository](https://github.com/GRID-is/api-sdk-py/tree/main/examples).
</Tip>

You will need to download the [simple goal seek example](https://github.com/GRID-is/api-sdk-py/blob/main/examples/goal_seek_example.xlsx) from us,
upload it to your GRID account and replace `REPLACE_WITH_YOUR_SPREADSHEET_ID` with its workbook id.
See our [quick start guide](https://docs.grid.is/api-reference/getting-started) for more details.

```python theme={null}
# /// script
# requires-python = ">=3.9"
# dependencies = [
#     "fastapi[standard]",
#     "grid-api",
#     "uvicorn",
# ]
# ///
import uvicorn

from fastapi import FastAPI
from grid_api import AsyncGrid, APIConnectionError, APIStatusError, RateLimitError

app = FastAPI()

@app.get("/seek_interests")
async def seek_interests(target_amount: float):
    client = AsyncGrid()

    try:
        response = await client.workbooks.query(
            id="REPLACE_WITH_YOUR_SPREADSHEET_ID",
            goal_seek={
                "targetCell": "Sheet1!C7",
                "targetValue": target_amount,
                "controlCell": "Sheet1!C5",
            },
            read=[]
        )
    except APIConnectionError as e:
        return {"error": "The server could not be reached."}
    except RateLimitError as e:
        return {"error": "A 429 status code was received; we should back off a bit."}
    except APIStatusError as e:
        return {"error": e.message}

    solution = response.goalSeek["solution"]

    return {"interest_rate": solution}


@app.get("/seek_years")
async def seek_years(target_amount: float):
    client = AsyncGrid()

    try:
        response = await client.workbooks.query(
            id="REPLACE_WITH_YOUR_SPREADSHEET_ID",
            goal_seek={
                "targetCell": "Sheet1!C7",
                "targetValue": target_amount,
                "controlCell": "Sheet1!C4",
            },
            read=[]
        )
    except APIConnectionError as e:
        return {"error": "The server could not be reached."}
    except RateLimitError as e:
        return {"error": "A 429 status code was received; we should back off a bit."}
    except APIStatusError as e:
        return {"error": e.message}

    solution = response.goalSeek["solution"]

    return {"years": solution}

if __name__ == "__main__":
    uvicorn.run(app, host="0.0.0.0", port=8000)
```

Make sure your [API key](https://app.grid.is/account/api-key) is set in the environment variable `GRID_API_TOKEN`, or passed as an argument to the `Grid` class.

<CodeGroup>
  ```python Using Python theme={null}
  client = Grid(api_key="REPLACE_WITH_YOUR_API_KEY")
  ```

  ```bash Using an environment variable theme={null}
  export GRID_API_TOKEN="REPLACE_WITH_YOUR_API_KEY"
  ```
</CodeGroup>

To start the goal seek server, run the following:

```term theme={null}
uv run goal_seek.py
```

Open the URL below to see how high the interest rate would need to be to reach \$150,000:

[http://localhost:8000/seek\_interests?target\_amount=150000](http://localhost:8000/seek_interests?target_amount=150000)

You should get a response like:

```json theme={null}
{"interest_rate":0.08713616268663185}
```

To see how many years it would take to save up \$200,000:

[http://localhost:8000/seek\_years?target\_amount=200000](http://localhost:8000/seek_years?target_amount=200000)

You should get a response like:

```json theme={null}
{"years":12.93949339333381}
```