I found this code for computing rate of APR and it works fine for me until i put something like

- Amount borrowed to be 2000
- return in 20 years time.
- baserate is 15%

and i get APR of -100 and so on.

```
function rate(paymentsPerYear, paymentAmount, presentValue, futureValue, dueEndOrBeginning, interest)
{
//If interest, futureValue, dueEndorBeginning was not set, set now
if (interest == null)
interest = 0.01;
if (futureValue == null)
futureValue = 0;
if (dueEndOrBeginning == null)
dueEndOrBeginning = 0;
var FINANCIAL_MAX_ITERATIONS = 128;//Bet accuracy with 128
var FINANCIAL_PRECISION = 0.0000001;//1.0e-8
var y, y0, y1, x0, x1 = 0, f = 0, i = 0;
var rate = interest;
if (Math.abs(rate) < FINANCIAL_PRECISION)
{
y = presentValue * (1 + paymentsPerYear * rate) + paymentAmount * (1 + rate * dueEndOrBeginning) * paymentsPerYear + futureValue;
}
else
{
f = Math.exp(paymentsPerYear * Math.log(1 + rate));
y = presentValue * f + paymentAmount * (1 / rate + dueEndOrBeginning) * (f - 1) + futureValue;
}
y0 = presentValue + paymentAmount * paymentsPerYear + futureValue;
y1 = presentValue * f + paymentAmount * (1 / rate + dueEndOrBeginning) * (f - 1) + futureValue;
// find root by Newton secant method
i = x0 = 0.0;
x1 = rate;
while ((Math.abs(y0 - y1) > FINANCIAL_PRECISION)
&& (i < FINANCIAL_MAX_ITERATIONS))
{
rate = (y1 * x0 - y0 * x1) / (y1 - y0);
x0 = x1;
x1 = rate;
if (Math.abs(rate) < FINANCIAL_PRECISION)
{
y = presentValue * (1 + paymentsPerYear * rate) + paymentAmount * (1 + rate * dueEndOrBeginning) * paymentsPerYear + futureValue;
}
else
{
f = Math.exp(paymentsPerYear * Math.log(1 + rate));
y = presentValue * f + paymentAmount * (1 / rate + dueEndOrBeginning) * (f - 1) + futureValue;
}
y0 = y1;
y1 = y;
++i;
}
return rate;
}
```

upon debugging, i found (maybe i am wrong) something happens when code hit, the bold part of

```
y = presentValue * f + paymentAmount * (1 / rate + dueEndOrBeginning) * (f - 1) + futureValue;
```

**-1 + futureValue**

what can be wrong?