This page explains how GPA Vault's calculators are built and kept accurate — the formulas we use, where the underlying numbers come from, and how often each one gets checked.
Our GPA, grade, and semester calculators use the standard weighted-average formula used by the overwhelming majority of US high schools and colleges: total quality points (grade value × credit hours, summed across courses) divided by total credit hours. Letter-grade-to-point conversions follow the common 4.0 scale (A=4.0, A−=3.7, B+=3.3, and so on).
Where a school-specific variation exists — for example, weighted GPA bonuses for AP, IB, or Honors courses (typically +0.5 to +1.0 depending on the school) — we state the most widely used convention explicitly and note that individual schools may weight differently. We don't present a single school's policy as universal.
SAT and ACT scaled-score and percentile conversions are based on publicly published concordance tables from the College Board and ACT, Inc. Percentile rankings reflect the most recent national testing cohort data these organizations have released. Because percentile tables are revised periodically as new cohorts test, we re-check these figures against the official sources whenever a new testing year's data becomes publicly available.
Loan payment, interest, and amortization calculations use the standard fixed-rate amortization formula used by federal loan servicers: monthly payment = P × r × (1+r)ⁿ ÷ ((1+r)ⁿ − 1), where P is principal, r is the monthly interest rate, and n is the number of payments.
Default interest rates shown on these calculators reflect the official federal Direct Loan rates published by the U.S. Department of Education following the annual May 10-year Treasury auction, which sets rates for loans first disbursed between July 1 and June 30 of the following year. These default rates change every July 1 when new-year rates take effect — we update the defaults and worked examples on this schedule, and a loan disbursed in a prior year keeps the rate it was originally given regardless of what the calculator's default shows today.
Repayment plan details (Standard, IBR, PAYE, RAP, and similar) reflect current federal program rules as published by the Department of Education and studentaid.gov. Federal student loan policy has changed materially in 2026 (the SAVE plan's replacement by RAP, and updated eligibility rules for PLUS loans) — we track these changes and update affected pages when official rule changes take effect, not on a fixed schedule, since policy changes don't happen on a predictable calendar.
Cost-of-attendance figures, aid formulas, and ROI comparisons are based on publicly available federal financial aid formulas (FAFSA methodology) and published national or major-specific averages from sources such as the Department of Education, NCES, and Bureau of Labor Statistics wage data. Where we cite "average" figures (starting salary by major, average debt by major, etc.), these are drawn from the most recent publicly available datasets at time of writing, not our own survey data.
We don't invent statistics, fabricate citations, or present a single school's or lender's policy as a universal rule. Where numbers vary by institution — GPA weighting, IB-to-GPA conversion, specific aid formulas — we say so explicitly rather than picking one convention and presenting it as the only answer.
If you find a calculation error or an outdated figure, email us at canghun13@naver.com. We check and correct reported errors as they come in, and update rate-dependent pages on the annual schedule described above.
Editorial Policy — how we write and review content on this site.