A method for determining a protection level of a position estimate using a single epoch of GNSS measurements, the method includes: specifying a prior probability density P(x) of a state x; specifying a system model h(x) that relates the state x to observables z of the measurements; quantifying quality metrics q associated with the measurements; specifying a non-Gaussian residual error probability density model ƒ(r|θ, q) and fitting model parameters θ using a set of experimental data; and defining a posterior probability density P(x|z, q, θ); estimating the state x; and computing the protection level by integrating the posterior probability density P(x|z, q, θ) over the state x.