India's GST system uses multiple rate slabs rather than a single flat tax, which trips up a lot of people trying to work out a final price by hand.
The slab structure
GST in India is commonly applied at rates including 5%, 12%, 18% and 28%, with different categories of goods and services assigned to different slabs — essential items generally sit at lower rates, while luxury or "sin" goods sit at the higher end. There are also specific exemptions and special rates for certain categories outside this standard structure. Because rates and category classifications are periodically revised by the GST Council, always check the current official rate for your specific product or service rather than assuming a rate stays fixed indefinitely.
GST-inclusive vs GST-exclusive pricing
A price can be quoted either before tax (exclusive) or after tax (inclusive), and confusing the two leads to real pricing mistakes — a ₹1,000 price plus 18% GST is not ₹1,180 calculated the same way as extracting 18% from a ₹1,180 GST-inclusive price, since the second calculation needs to work backward from the total, not simply take 18% off it.
Calculate both directions correctly
A GST calculator handles both directions properly — add GST to a base price, or extract the base price and tax amount from a GST-inclusive total — at any of the standard slab rates, without the backward-calculation error that trips up manual math.
The bottom line
Knowing which slab applies to your specific item and whether you're working forward from a base price or backward from a final price are the two things that most often go wrong doing GST math by hand.
Try it yourself
Put this into practice with our GST calculator.