Formula to cover two criteria exclusively and together

[C_S_M_S]

Hopefully a straight forward one for you guys but please can someone help!

I want to do the following;
If column A has "Standard" and the date in Column B is below a chosen date then do one calculation. If column B has a date higher than the chosen date then do a different calculation. However if column A does not have "standard" then use the original calculation regardless of date.

I have tried an IF OR formula but it ignores one criteria and produces the wrong calculation for some of the dates.
I have tried an IF AND formula and this works while the column has "standard" in it, but when this is removed it does not work.

Please help!

 

[Special-K99]

Description is a little vague.
Use this

=IF(A1="Standard",IF(B1 < C1,calculation1,calculation2),original calculation))
(Remove spaces from around < as this forum corrupts the formula when it contains < or > )

where C1 is "chosen date"

 

[C_S_M_S]

Sorry for the vague description - first time using a forum like this! Thank you! It worked - I tried an embedded IF statement yesterday but I missed the final 'if false' part so it wouldn't work!

Thanks again - that is perfect!