Flashcards for mental math
Fast mental math is mostly memorized facts wired to fast retrieval, not clever tricks performed on the fly. Someone who "just knows" that 17² is 289 doesn't calculate it under time pressure — they've seen it enough times that it surfaces the way your own phone number does. Flashcards are the direct route to that: a deck of the facts that come up constantly, reviewed until they stop needing calculation at all.
Add a starter deckWhy memorized facts speed up calculation
Every mental math technique — splitting a multiplication, rounding then correcting, working with fractions — eventually bottoms out in a handful of base facts. If those facts are memorized, they're free: you spend zero working-memory budget on them and all of it on the technique itself. If they're not memorized, every technique gets slower and shakier, because part of your attention is stuck re-deriving 8 × 7 while the rest of you is trying to hold the bigger problem together.
This is exactly the gap flashcards close. A timed drill (see mental math practice) measures your current speed and rewards technique; a flashcard deck builds the raw recall that every technique depends on, at whatever pace spaced repetition decides you need.
The built-in starter decks
Flashcards ships with six starter decks built specifically for mental math. Add any of them from the empty-deck screen or the deck list, and they behave like any other deck — same FSRS scheduling, same stats, same Again/Hard/Good/Easy grading.
| Deck | Covers |
|---|---|
| Squares 1–30 | n² for every n from 1 to 30 (1 through 900) |
| Cubes 1–15 | n³ for every n from 1 to 15 |
| Powers of two | 2⁰ through 2²⁰ |
| Times tables 13–19 | The tables just past the usual 12×12 ceiling, where most people's recall gets shaky |
| Fraction–decimal | Halves through twelfths, both directions (½ ↔ 0.5, and back) |
| Percent shortcuts | Common percent-of-a-number facts (like 15% of 80) that come up constantly in tipping, discounts and estimates |
Squares and cubes are worth calling out specifically: once 13² through 17² are automatic, estimating square roots and spotting near-square products both get noticeably faster, because you're pattern-matching against known values instead of computing from nothing. See square numbers from 1 to 100 for the full table if you want to preview what's in the deck before adding it.
Flashcards versus timed drills — use both
These aren't competing tools. A flashcard deck is where a fact goes from "I can work it out" to "I just know it," reviewed at exactly the spacing that keeps it fresh without wasting time on facts you've already nailed. A timed drill in Math drills is where you find out whether that knowledge holds up under actual time pressure, mixed in with everything else. Many people get the best results running a starter deck for a few minutes a day and a timed drill separately to check that the speed is actually showing up in practice.
The times-tables starter deck pairs directly with times tables practice — memorize the individual facts in Flashcards, then use the timed test to confirm you can produce them fast and under pressure, not just recognize them slowly.
Pace yourself when adding a starter deck
Adding the squares or powers-of-two deck drops in dozens of new cards at once, and by default a deck only introduces a limited number of brand-new cards per day rather than throwing all of them at you the first session. That's deliberate — thirty new facts in one sitting would mean a long first review and a pile of same-day repeats. If a deck feels too slow to start, or you have a test coming up and want to front-load it, the deck settings let you raise the daily new-card limit; lower it again afterward if daily reviews start feeling long.
Building your own math facts deck
The starter decks cover the most commonly useful ranges, but nothing stops you from adding your own cards for whatever you personally find slow — a specific set of two-digit squares, a conversion table you keep looking up, or the exact percentages your job uses. Keep each card to one fact (see how to write flashcards that actually stick) and let the scheduler do the rest.
Where these facts show up outside the deck
The point of memorizing squares, cubes and powers of two isn't the flashcard session itself — it's what gets faster elsewhere. Estimating a square root starts by bracketing between two known perfect squares (see estimating square roots); that bracketing is instant once the squares themselves are memorized instead of half-remembered. Powers of two turn up constantly in anything involving doubling, file sizes or binary — knowing 2¹³ = 8,192 on sight saves a chain of doublings every time it comes up. None of that requires thinking about flashcards at all once the facts have settled in; they just stop being things you calculate.
Frequently asked questions
Do I need to add all six starter decks?
No — add whichever ones cover facts you don't already have memorized. Adding a deck full of things you already know just adds review time for no benefit.
Will this replace practicing mental math techniques?
No. Memorized facts make techniques faster to execute, but the techniques themselves — splitting, rounding, working left to right — are still worth learning separately. See mental math tricks.
How long until squares 1–30 feel automatic?
It varies by person, but because the scheduler shows each square right before you'd forget it, most people find the easy ones (5², 10², 12²) feel automatic within a couple of weeks, while unusual ones like 23² or 27² take longer simply because they come up less often day to day.
Add the squares deck