Break-even here is not a spreadsheet exercise; it is a confidence question. The annual rate is lower on every plan. The only reason to pay the monthly premium is to keep the right to walk away early.
When the annual plan is NOT the right call
Monthly billing is the better buy in one case: when there is a real chance you drop the tool in the first few months. A first CRM on a team that has never sustained one, a seasonal business, a pilot you have not sold internally yet: in each, paying monthly means you stop paying the day it does not work, and you never committed a full year per seat up front (Growth's annual commitment is US$468/seat/year per seat, paid now). That flexibility is worth the premium precisely when the outcome is uncertain. It is not worth it once the tool is part of how your team works.
The decision rule
Use your own history. If you have run any CRM for six months or more, you will keep this one, so commit annually and take the lower rate; there is no upside left in the monthly premium. If this is your first CRM and adoption is genuinely unproven, start monthly, put a date on the calendar, and switch to annual the moment it has stuck, usually within a quarter. Either way, size the commitment first in the cost worksheet, and if the annual-versus-monthly gap is the crux, the billing-cycle breakdown lays out every plan.