Usually for financial aid purposes, merit scholarships (whether internal or outside,) will not stack on-top of need-based aid. This is because NEED-based aid cannot replace your parents’ contribution (EFC as calculated by the school,) but you can utilize the merit scholarships (amount varies from school to school) to count towards your student contribution (expected pay from working during the school year/summer, some schools will allow for a 1-time computer purchase etc.)
Like most other top-LACs, Grinnell meets every student’s full demonstrated need (https://www.grinnell.edu/admission/financial-aid/understanding-your-award ) but the definition of this need varies WIDELY from college to college, based on the school’s own resources, the formulas they use etc.
The only exception to this would be if you received a merit scholarship award that was higher than your need-based aid award, meaning you will receive the full amount of the scholarship award and likely none of the need-based aid (because the scholarship award counted against it.)
While you don’t usually have a say in how internal merit scholarship aid will be disbursed, you DO have a say in how outside merit-scholarship aid will be sent to the college. If you receive more outside merit scholarship aid than you can waive your contribution with, it would be beneficial to ask the scholarship provider if they can defer their payment to a later year (or spread it over multiple years,) in-order to maximize your benefit from it.
Ex: Bob receives 25K in need-based aid from his college, and his parents are expected to pay $55K. He also receives a $5K merit scholarship award. Bob’s school allows him to waive the entirety of his student contribution ($3K,) but he still has $2K left. As this cannot count towards his parent’s payment of $55K, $2K of his need-based aid is REPLACED with merit scholarship, leaving him with $28K of aid in total, NOT $25+5K.
As other posters have commented, while the financial aid calculators on school websites are a helpful ESTIMATE of expected aid awards, they are not a guarantee. The Fianancial Aid Office at Grinnell has the last word on how much and in what manner aid is offered to you, but you can always appeal your award if admitted ED and the offered award is vastly different from that of the calculator.
Hope that helps! Good luck with admissions!