Aid is annual, so a gap year re-bases the calculation rather than pausing it. An award year is defined at 34 CFR 600.2 as "the period of time from July 1 of one year through June 30 of the following year", and 20 U.S.C. 1090(a)(1) requires each individual seeking federal aid "for award year 2024-2025 and any subsequent award year" to file the Free Application for Federal Student Aid. There is no carry-over. An application filed for a year the student does not attend produces nothing that survives into the next one, and the student files again for the year they actually enroll.
Which tax year gets measured changes, and that is the whole planning point. 20 U.S.C. 1087vv(a) defines total income as adjusted gross income "for the second preceding tax year" plus untaxed income and benefits minus excludable income for the same year. Section 1090(d)(4)(A) requires the Department to open the application "not later than October 1 prior to the applicant's planned year of enrollment", which is a duty on the Department rather than a student deadline. So a student who defers entry by one year is measured on a tax year one later than they would otherwise have been. Whether that helps depends entirely on which direction the family's income moved, and the answer is knowable in advance because the relevant tax year is already in the past by the time the application opens.
Gap-year earnings are the student's income, and student income is assessed hardest. Under 20 U.S.C. 1087oo(g)(1) a dependent student's available income is total income minus an adjustment, multiplied by 50 percent, floored at zero from the 2025-2026 award year onward. The adjustment at (g)(2) subtracts federal income taxes, an allowance for payroll taxes and an income protection allowance the Secretary adjusts annually. Compare the parents' side, where available income and available assets are combined and run through the assessment schedule at 1087oo(e), which tops out at 47 percent. So a dollar of the student's earnings above the allowance is assessed at a higher rate than any dollar of the parents'. A gap year spent working full time is capable of raising the Student Aid Index materially for the first year of enrollment, and the effect lands two years later, which is exactly when nobody is expecting it.
Where the money is kept matters as much as how much of it there is. Section 1087oo(h) provides that "the student's assets are determined by calculating the assets of the student and multiplying such amount by 20 percent", with no protection allowance. Parents' assets, by contrast, are reduced by an age-based asset protection allowance and then counted at 12 percent under 1087oo(d)(1)(A), before entering the progressive schedule. Gap-year savings sitting in a bank account in the student's own name are therefore counted harder than the same balance in a parent's account, and this is one of the few places in the formula where a decision about titling has a direct arithmetic effect.
For a student already enrolled with federal loans, a gap year spends something that cannot be re-earned. Under 34 CFR 685.207(b)(2)(i) and (c)(2)(i), when a borrower ceases to be enrolled on at least a half-time basis, "a six-month grace period begins, unless the grace period has been previously exhausted". There is one grace period per loan, not one per interruption. A gap year longer than six months runs it out and the loan enters repayment. Returning to school puts the borrower back into an in-school period and can be granted an in-school deferment under 34 CFR 685.204(b), which is the right tool, but on final graduation there is no second six-month grace period waiting. A gap year of six months or less taken between academic years, with enrollment resuming before the period ends, is a different matter, which is why the length of the gap and not the fact of it is what decides the cost.
Two things a gap year does not do. It does not affect federal aid eligibility as such, since eligibility is tested each year on that year's facts. And it does not create any federal right to hold an admission offer or an institutional award. Deferred admission and whether a merit scholarship survives a deferral are institutional policies, decided college by college, and they are the two questions to get in writing before committing to the year.