Blog — Gpakit

The Gpakit blog covers the math behind the calculators on this site. Each post walks through one formula — how GPA is actually computed, what the SAT-ACT concordance does and doesn't claim, why four 25-minute Pomodoro blocks produce better focus than two hours straight — and points to the calculator that runs the arithmetic once you've understood it. The posts are written for readers who want to see the formula before trusting the result, which turns out to be most of the people who email us.

Every post cites its primary sources by name: College Board data updates, registrar handbooks, peer-reviewed psychology papers, federal student aid regulations. Where a rule is known to shift year to year (AP cutoffs, FAFSA Student Aid Index parameters, 529 rollover provisions), we flag that on the page. When a reader writes in with a correction we can verify, the post gets updated and a short note gets added to the relevant calculator's changelog.

GPA & grade mechanics

How the numbers on your transcript are produced, and why two students with identical letter grades can end up with different GPAs.

How GPA is actually calculated: the arithmetic behind your transcript

Most students have never seen the simple credit-weighted average hiding inside every semester GPA. Here is the math, worked step by step.

Weighted vs unweighted GPA: what colleges actually see

Admissions offices routinely recalculate your GPA their own way. Here is what that means for how you should think about AP and Honors courses.

Class rank and percentile: what the number on your transcript actually means

Class rank is a position; percentile is a ratio. Why the difference matters to admissions offices and how to read both on your own transcript.

Exams & scoring systems

Weighted-average math, annual cutoff shifts, and percentile-based concordance — the three places exam scoring gets unintuitive.

SAT to ACT concordance: how the College Board conversion table works

The official 2018 concordance table is a percentile-rank crosswalk, not a direct score swap. Why that distinction matters for application strategy.

The math behind "what do I need on my final?"

One straightforward weighted-average formula answers the single most-searched grade question in America every December and May.

How AP exam scoring works: composite scores, score bands, and why predictions wobble

AP exams run on a weighted composite of multiple-choice and free-response sections, with cutoffs that shift each year. Here is how the math lines up.

How learning actually works

What the research actually supports about attention, spaced repetition, and the credit-hour study rule — separating the evidence from the marketing.

The Pomodoro technique: what the research actually says about 25-minute blocks

Timed work intervals can improve focus, but the optimal interval length depends on task type and individual working memory. Here is what the evidence supports.

Spaced repetition: the forgetting-curve math that makes flashcards work

Ebbinghaus's 1885 retention data still drives the interval formulas in every flashcard app. A plain walk through how SM-2 picks your next review date.

How many hours should you actually study? The credit-hour rule, examined

The "two to three hours per credit hour per week" guideline has been around for a century. What does the evidence say about whether it is still right?

College admissions & money math

How admissions offices read GPA in tier, and how the compound-interest math behind a 529 plan actually plays out over eighteen years.

Minimum GPA requirements by college tier: a data-driven breakdown

Selective, target, and safety schools each carry distinct GPA floor expectations. How to read them honestly alongside test scores and course rigour.

Saving for college: the compound-growth math that decides your 529

How a 529 plan turns $3,000 a year into six figures by the time a kindergartener graduates high school — and the assumptions that drive the number.

Math fundamentals that keep showing up

Why sig-fig rules that feel arbitrary in class are really rules for not over-reporting measurement precision.

Significant figures in academic work: the rules that keep showing up on exams

Sig fig rules feel arbitrary until you realise they're a shorthand for measurement uncertainty. The five rules, explained with worked examples.