Priya's portfolio app pings her with good news: the company she's held for two years just announced a 1:1 bonus issue. Her 100 shares are about to become 200. She opens the app expecting to feel richer. Instead, the price chart shows an overnight drop of nearly 50%, and her total portfolio value hasn't moved an inch. Twice the shares, and somehow it feels like she got robbed.
Wait, Your Money's Still There
Nobody took anything from Priya. A bonus issue is a company handing existing shareholders extra shares for free, in a fixed ratio, funded by converting its own accumulated profits into share capital. No new cash changes hands, and nothing about the company's factories, revenue, or bank balance changes overnight. So when the number of shares in circulation doubles, the exchange divides the price by roughly the same amount on the same day, and the two changes cancel out.
The math here is almost insultingly simple: twice the shares at roughly half the price is still the same amount of money. A bonus issue doesn't make a company worth more. It just changes how many pieces that same worth gets counted in.
Think of It Like Cutting a Cake Into More Slices
Imagine a birthday cake cut into 8 equal slices, and you own 1 slice, an eighth of the whole cake. Now imagine the host walks over and recuts the exact same cake into 16 slices. You get handed a second slice. You now own 2 slices instead of 1, but 2 out of 16 is exactly the same eighth of the cake you had before. Nobody baked more cake. Nobody ate any less. The knife just moved.
A bonus issue is that recut, applied to a company's ownership instead of dessert. The "1:1" in a 1:1 bonus issue is just the recipe for how much smaller each new slice is.
Here's the Actual Math, With a Real Stock
Numbers make this easier to trust than analogies, so here's an actual bonus issue instead of a hypothetical one. BSE Ltd (the exchange itself, coincidentally) announced a 2:1 bonus issue in 2025, meaning 2 new shares for every 1 already held, fixing a record date of May 23, 2025. The stock had closed the previous session at ₹6,996.5.
On the ex-date, the day the adjustment actually happens, exchanges apply a fixed formula: divide the pre-bonus price by (bonus ratio + 1). For a 2:1 bonus, that's ₹6,996.5 ÷ 3, which comes out to roughly ₹2,332. BSE's stock actually opened that day around ₹2,335 and traded up from there, landing almost exactly where the formula predicted. A shareholder who held 100 shares worth ₹6,99,650 the day before woke up holding 300 shares worth close to the same amount. Nobody's holding shrank. The price tag on each individual share did.
What People Get Wrong About Bonus Issues
A bonus issue means the company gave you free money.
The company converted reserves it already had, built from its own profits, into shares you already had an economic claim on. If converting your own savings into a different denomination counted as a windfall, changing a ₹500 note into five ₹100 notes would make you richer too.
A stock crashing right after a bonus issue is a red flag, time to sell.
The drop is the exchange doing arithmetic, not the market losing confidence. Compare the price to the formula above before assuming anything is wrong.
Myth: A bonus issue and a stock split are basically the same thing. Reality: Both increase your share count and cut the price proportionally, but a bonus issue uses up company reserves and leaves the face value of each share untouched, while a stock split touches no reserves at all and specifically cuts the face value itself. A company signaling confidence in its reserves reaches for a bonus issue; a company mainly trying to make its stock more affordable per share reaches for a split.
Where to Go From Here
Priya's story ends the same way every bonus issue does: no richer, no poorer, just holding more paper that adds up to the same number. That's genuinely most of what you need to know before you stop panic-refreshing your portfolio app.
What this piece skipped on purpose: the exact SEBI timeline a company has to follow to pull this off, what happens to your bonus shares if you eventually sell them (there's a specific, slightly odd tax rule for that), and how a bonus issue stacks up against a stock split or a straight-up dividend when you're trying to read what a company is actually signaling. TraderStack's full breakdown covers all three.