Before we get into those more sophisticated approaches to measurement, it is worth mentioning one helpful rule of thumb: in the long run, the neutral real rate is highly likely to be positive. This is because of time preference. People would rather have a dollar now than a dollar tomorrow or next year.
They demand some compensation for having to wait, even if the payoff next year is risk-free. Because the policy rate represents the risk-free short-term interest rate, it embeds people’s underlying time preference. So we should expect the neutral real rate also to be positive, though it could be small.