Tested in November 2026. Bill creation, the keypad, the keyboard input, the timer, the scoring and the daily set were tested in a desktop browser. The game makes sure every final amount is a whole number of rupees.
How to play the Mental Bill Challenge
- Press Play now, or choose Aaj ka challenge for the same five bills everyone gets today.
- Read the items. Each line shows the quantity, the item and the price of one.
- Apply the discount or coupon. Later bills also add GST.
- Type the final amount with the keypad or your keyboard and press OK. You have 30 seconds.
- After five bills you see your points, your average time and a share card.
Quick mental maths tricks
| Situation | Shortcut |
|---|---|
| 10 percent off | Move the decimal point one place and subtract. |
| 20 percent off | Take 10 percent and double it, then subtract. |
| 25 percent off | Take a quarter of the total and subtract. |
| 50 percent off | Halve the total. |
| 5 percent GST | Take 10 percent, halve it and add. |
Tips to score higher
- Add up the item lines first, then apply the discount.
- Round prices in your head, for example 45 as 50 minus 5, and fix it at the end.
- GST is added after the discount, on the reduced amount.
- If you are short on time, a close guess earns nothing, so use the time to be exact.
Limits to know about
- Every answer must be exact. A near answer is marked wrong.
- Prices are made up by the game and are not real shop prices.
- GST and discounts follow the rules shown on the screen and are not tax advice.
Privacy
The game runs in your browser. Nothing is sent to a server. Your best score, streak and sound choice are stored on this device only.
Frequently asked questions
What is Aaj ka challenge?
It gives everyone the same five bills on the same date. Finish it on consecutive days to build a streak.
How are points worked out?
A right answer is worth up to 100 points. You lose 2 points for every second you take, but never go below 40 for a right answer.
Is GST added before or after the discount?
In this game GST is added after the discount, on the amount left.
Can I use a calculator?
You can, but the game is meant to train mental maths. For real bills, use our GST and discount calculators.
Mental Bill Challenge is a free game from ToolsRiver. No sign-up. More games are in the Gaming Tool section.