Can someone tell me how to derive the relationship between currency futures and the corresponding spot forex pair quotes? For example, if I think USDJPY would hit 123.00 and reverse, how can I derive the corresponding 6J M7 price when USDJPY hits 123.00? I think it is a function of the interest rates of these two currency as well as the number of remaining days to the futures contract expiration day. Can someone give me a general formula? Besides the factor of interest rates, is there any other factor may affect the relation? Thanks in advance.