User guide

How every figure is worked out

Every figure on every screen, and exactly how it is arrived at. If a total here does not match a total on your screen, that is a bug worth reporting — these are the rules the software actually follows, written from the code that does the arithmetic.

The order things happen in

On a sale and on a purchase alike, the order is the same, and it is the order GST law sets out:

Line value = price × quantity.
Less the line's discount — a percentage, or an amount you typed, which is turned into its percentage of that line.
Less the bill's own discount, spread across the lines in proportion to their value.
What is left is the taxable value. GST is charged on this, not on the price before discount — the supply is taxed on what is actually payable for it (CGST Act s.15(3)(a)).
GST at the rate the item's HSN carries on the date of the bill.
Round off to the nearest rupee, and
Net total — what the customer pays, or what the supplier is owed.

So: discount first, GST second. A ₹1,000 saree with 10% off and 5% GST is ₹900 taxable, ₹45 GST, ₹945 payable — never ₹1,050 less 10%.

Which GST, and how much

The rate comes from the item's HSN code and the rules in force on the date of the bill. A rate that changes next month does not change a bill already raised.
A rule may be banded by price — 5% up to a threshold and 12% above it — and the band is chosen per line, on the line's taxable value.
Within your state: CGST and SGST, each half the rate. 5% is 2.5% + 2.5%.
To another state: IGST at the full rate. Which state is decided by the place of supply — the customer's GSTIN for a registered buyer, otherwise your own state.
The halves are split so they always add back to the total: an odd paisa goes to CGST.

Rounding

Money is held to four decimal places throughout and only rounded where a rule says to, so a long bill does not drift a paisa at a time.
The net total is rounded to the nearest rupee; the difference is shown as Round off and posted to its own ledger, so the books still balance to the paisa.
A percentage is applied half-up: ₹0.125 becomes ₹0.13.

On a sale

Item discount — per line, as a percentage or an amount. Above the shop's cap it needs a manager's approval.
Bill discount — on the whole bill, as a percentage or an amount.
Markdowns and clearance prices replace the price before any discount is applied; the label says which is in force.
A government rebate is applied per line at the rate the scheme sets, and is shown separately from a counter discount: it is the government's money, not the shop's, and is claimed back later.
Payments may be split across cash, card, UPI and credit. Change due is what the customer over-tendered in cash.

On a purchase

Line discount — the trade discount the supplier gave, off before tax as above.
Freight and carriage the supplier has charged is added to the bill with its own GST rate, posted to its own ledger (Freight and carriage inward) so a year's delivery cost can be read on its own. Its input tax is claimed on the same invoice.
Input GST is recorded by head — CGST, SGST, IGST — because GSTR-3B claims each separately.
A supplier with no GSTIN cannot charge GST and none can be claimed: enter the rate as 0% and the whole amount is the cost of the goods.
A debit note (goods sent back) reverses exactly what that line claimed — never a fresh calculation.

On a return

A credit note credits the tax that was charged on the original bill, at that bill's rate, even if the rate has changed since.
Part of a line comes back pro rata: three sarees of five is three fifths of that line's taxable value and of its tax, to the paisa, with the last piece taking any remainder so the notes add back to the bill exactly.
The credit is applied first to whatever is still owed on that bill, and only what is left is refunded or kept on account.

Stock and cost

Quantities are held in the smallest unit: pieces as counted, cloth in centimetres, yarn in grams. Nothing is ever stored as a fraction.
Stock on hand is the sum of every movement at that branch — receipts, sales, returns, transfers, adjustments — never a running figure that can drift.
Stock value is at cost: what was paid for it, from the goods receipt or purchase bill.

In the books

Every document posts a balanced voucher: total debits equal total credits, or nothing is written at all.
Nothing is ever edited or deleted. A correction is a reversal: a second voucher that answers the first line for line, with both kept.
A customer's balance is their ledger: bills and debits less receipts, credit notes and allocations. What a report shows is what the ledger says — no report computes a balance of its own.