Try these formulas. I arrived at these by using a little algebra. They aren't official but, they should be close if all credit factors are equal.
Experian to Fico conversion 850 - ((990 - Experian Score/489) * 550) = estimated Fico Score
Fico to Experian conversion 990 - ((850 - Fico Score/550) * 489) = estimated Experian Score
Completely different Algorithm based upon the same data. The best correlation will be to say that they are more likely to move in the same direction than different directions, at least for large movements.
For my education, I have now tracked 83 Vantage score changes during a period of two FICO changes.
Trying to come up with a formula is a waste of time.
There is no relationship. They take the same data (hopefully) but weight it differently. There is theefore no constant formulka to go from one to the other. It is not like going from Fahrenheit to Centigrade.
VantageScore and FICO scores are both legitimate scores that are reasonably good at predicting risk given a large population of samples. That does NOT mean that they will predict risk the same or even at all close to the same for any given individual.The best way to convert one score to another is not to use a formula but to convert the score to its rank ordered percentile then use the same percentile to map to the other score. That's as good as it gets which unfortunately isn't very good. There simply is a very large variance between individuals rank order amongst the various "scores" out there.
For instance I had a FICO rank score of 41% at the same time I had a VantageScore rank of 91% derived from exactly the same CRA file. These are both legitimate lender used scores, albeit VantageScore isn't used my very many. Now imagine what the differences could be with FAKOs such as Score Plus that are only sold to consumers.