user127819: A quick google search told me that up to today, more than 18.78 million bitcoins have been mined. Source
Another google search told me that today, the mining reward is 6.25 bitcoin per block.
If the above data is correct, I wonder why my calculation doesn't add up:

According to the rules by Nakamoto, the reward becomes half after every 210,000 bitcoins are mined.
The initial reward is 50 BTC/block, but now the reward is 6.25 BTC/block, this means the reward has been cut in half 3 times, meaning around 630,000 to 840,000 bitcoins have been mined.

Then how come the first link tells me it's 18.78 million? I must have done something wrong. Please point it out. Thank you!

Edits:
I know where I'm wrong now. "210,000 bitcoins are mined" aren't correct; it's supposed to be 210,000 blocks

user208: 
The first 210000 blocks permitted mining up to 50 BTC each. That's 50 * 210000 = 10500000 BTC, or 10.5M BTC in total at block 210000.
The second 210000 blocks permitted mining up to 25 BTC each. That's 25 * 210000 = 5250000 BTC, or 15.75M BTC in total at block 420000.
The third 210000 blocks permitted mining up to 12.5 BTC each. That's 12.5 * 210000 = 2625000 BTC, or 18.375M BTC in total at block 630000.
The fourth 210000 blocks permit mining up to 6.25 BTC each, but as of writing, only 75572 such blocks have been mined. That's 6.25 * 75572 = 472325 BTC, or 18.847M BTC in total at block 705572.

The actual number is slightly lower due to various reasons where coins have been failed to be claimed, or burned. See https://bitcoin.stackexchange.com/a/38998/208 for details on various ways this has happened.

127819: <p>A quick google search told me that up to today, more than 18.78 million bitcoins have been mined. <a href="https://gadgets.ndtv.com/cryptocurrency/features/bitcoin-total-coins-limit-21-million-price-impact-mining-2512575" rel="nofollow noreferrer">Source</a></p>
<p>Another google search told me that today, the mining reward is 6.25 bitcoin per block.</p>
<p>If the above data is correct, I wonder why my calculation doesn't add up:</p>
<ul>
<li>According to the rules by Nakamoto, the reward becomes half after every 210,000 bitcoins are mined.</li>
<li>The initial reward is 50 BTC/block, but now the reward is 6.25 BTC/block, this means the reward has been cut in half 3 times, meaning around 630,000 to 840,000 bitcoins have been mined.</li>
</ul>
<p>Then how come the first link tells me it's 18.78 million? I must have done something wrong. Please point it out. Thank you!</p>
<hr />
<p>Edits:</p>
<p>I know where I'm wrong now. &quot;210,000 bitcoins are mined&quot; aren't correct; it's supposed to be 210,000 <strong>blocks</strong></p>
 208: <ul>
<li>The first 210000 blocks permitted mining up to 50 BTC each. That's <em>50 * 210000 = 10500000 BTC</em>, or <em>10.5M BTC</em> in total at block 210000.</li>
<li>The second 210000 blocks permitted mining up to 25 BTC each. That's <em>25 * 210000 = 5250000 BTC</em>, or <em>15.75M BTC</em> in total at block 420000.</li>
<li>The third 210000 blocks permitted mining up to 12.5 BTC each. That's <em>12.5 * 210000 = 2625000 BTC</em>, or <em>18.375M BTC</em> in total at block 630000.</li>
<li>The fourth 210000 blocks permit mining up to 6.25 BTC each, but as of writing, only 75572 such blocks have been mined. That's <em>6.25 * 75572 = 472325 BTC</em>, or <em>18.847M BTC</em> in total at block 705572.</li>
</ul>
<p>The actual number is slightly lower due to various reasons where coins have been failed to be claimed, or burned. See <a href="https://bitcoin.stackexchange.com/a/38998/208">https://bitcoin.stackexchange.com/a/38998/208</a> for details on various ways this has happened.</p>
