Math practice · reimagined
Interest
Turn Interest into a fight you actually want to win. Every problem is an attack — solve it faster than your opponent and you land the hit.
Ages 4–99+ · no download · plays in your browser · 23 languages
How it works
Interest
Pick a fighter, choose Interest, and trust your numbers. The faster and cleaner you solve, the harder you hit — from gentle early grades all the way to Olympic-level challenges.
Interest is what money earns for being lent out — or costs for being borrowed. Simple interest is the straightforward version: the same amount is earned every single year, because it is always worked out on the ORIGINAL sum.
Three things decide it. The principal P is what you started with. The rate r is the percentage earned per year. The time t is how many years it sits there. Multiply all three: I = P × r% × t.
Put £400 in at 5% for 3 years. Five percent of 400 is 20, so it earns £20 each year, and over three years that is £60. That is the interest — the account now holds £460, but the question asked what it EARNED, not what it holds. Read carefully which one is wanted.
Real bank accounts usually pay compound interest, where each year's earnings start earning too, so the total creeps ahead of this. Simple interest is the honest first model, and it is still exactly how many loans are quoted.
Find one year's interest, multiply by the number of years, and type the total interest earned.
Every level of Interest
— Quick answers —
Interest: the short FAQ
- Is Interest free to play?
- Yes. Interest is free to play right in your browser — the whole curriculum, no download, no signup. Paid plans later unlock the full fighter roster, every stage and saved progress.
- Who is Interest for?
- Anyone from 4 to 99+. The early grades stay gentle for beginners, while the higher tiers will make even the confident sweat.
- Do I need to download anything to play Interest?
- Nope. Interest runs in any browser, on a laptop, tablet or phone.
- Can Interest be used in the classroom?
- Absolutely. Teachers run Interest with a whole class and track who's improving — see the schools plan for per-student pricing and a teacher dashboard.