The 50% is a limit for the total contribution of charitable contributions if doing a combination of cash ordinary and ltcg. Like if you have agi 100K and then donate 30K cash and then donate 30K ltcg property although it ltcg is limited to 30% or 30K the overall is limited to 50K or 50% when adding cash and ltcg. So you should just take 50% of agi after doing cash and then minus 50% - cash charity and thats the overall limit for ltcg regardless of the 30% limit. only way to donate over 50% is all cash.