Currently, setting a custom budget that repeats every 2 weeks or every 15 days doesn't work for income received on set days twice a month (eg. on the 15th and 31st), because not all months have the same number of days. This means that instead of consistent periods from 31st-14th and 15th-30th, you end up with 31st -13th, 14th-27th, 28th-10th, and so on.

The semi-monthly (or twice a month) option would take different month lengths into consideration and repeat consistently based on two anchor days (eg. new budget every 15th and 31st). 31st would automatically be the 30th or 28th instead depending on the month.