Other useful resources: How to Change Your Mind, (annotated summary); Phases of an LSD Trip; Precise dosing of LSD; How to Find a Psychedelic Guide

The following chart is a non-scientific estimation of LSD tolerance.  It was based on several users' subjective experiences.  Do not put un-due reliance on this!  

Some have reported it over-estimates tolerance (you need less than the graph would suggest).  Many have reported this is a helpful starting point.  

Approximation formula:

y= x/100*280.059565*n^-0.412565956   

Y represents dosage needed for same effect

x represents last dosage taken

N value represents the number of days since last trip.