Can anyone tell me how to calculate the phase delay of this simple one pole filter? (I HATE filter math)

Thank you.

```
class OnePole
{
public:
OnePole()
{
a1 = 1.0f;
b0 = 0.0f;
z = 0.0f;
gain = 1.0f;
}
~OnePole(){}
inline void setLowPass(float freq, float sampleRate)
{
jassert (sampleRate > 0.0);
jassert (freq > 0.0 && freq <= sampleRate * 0.5);
a1 = std::expf(-2.0f * juce::float_Pi * (freq / sampleRate));
b0 = 1.0f - a1;
}
void clear()
{
z = 0.0f;
}
void setGain(float g)
{
gain = g;
}
inline float tick(float in) noexcept
{
auto x = in * gain;
return z = b0 * x + a1 * z;
}
private:
float a1, b0, z, gain;
};
```