Compound Interest

By many accounts, compound interest is considered the eighth wonder of the world. So what is the big deal about it. Here is a story and I thought of validating and quantifying it. Here it goes -

The Legend of ChessBoard

Once upon a time, {come on! I had to start like that ;-)} there lived a king. He had acres and acres of land under his rule with bountiful crop year after year.

One day, a courtier gifted the king with a beautifully crafted hand-made chessboard. It was indeed one of its kind, and the king was very much impressed with the art work and detailing present in chessboard. So the king asked the courtier - what will he have in return? And the courtier requested rice grains in return to the tune of the rice that can be collected by placing one rice grain on the first square, two rice grains on the second square, four rice grains on the third square, so on and so forth until the sixty-fourth square of the chessboard.


The king laughed it out, and asked his men to immediately give the courtier his requested number of rice grains. But even after days of calculation and months assessment the king could not fulfil this simple request and finally gave up.

So what was the quantity the courtier really requested? Let's deep dive with an excel sheet -


Square # Rice Grains Weigh (gm) Sum@Sq# (gm)
1 1 0.03
2 2 0.05
3 4 0.10
4 8 0.20
5 16 0.40
6 32 0.80
7 64 1.60
8 128 3.20
9 256 6.40
10 512 12.80
11 1024 25.60
12 2048 51.20
13 4096 102.40
14 8192 204.80
15 16384 409.60
16 32768 819.20 1638.38
17 65536 1638.40
18 131072 3276.80
19 262144 6553.60
20 524288 13107.20
21 1048576 26214.40
22 2097152 52428.80
23 4194304 104857.60
24 8388608 209715.20
25 16777216 419430.40
26 33554432 838860.80
27 67108864 1677721.60
28 134217728 3355443.20
29 268435456 6710886.40
30 536870912 13421772.80
31 1073741824 26843545.60
32 2147483648 53687091.20 107374182.38
33 4294967296 107374182.40
34 8589934592 214748364.80
35 17179869184 429496729.60
36 34359738368 858993459.20
37 68719476736 1717986918.40
38 137438953472 3435973836.80
39 274877906944 6871947673.60
40 549755813888 13743895347.20
41 1099511627776 27487790694.40
42 2199023255552 54975581388.80
43 4398046511104 109951162777.60
44 8796093022208 219902325555.20
45 17592186044416 439804651110.40
46 35184372088832 879609302220.80
47 70368744177664 1759218604441.60
48 140737488355328 3518437208883.20 7036874417766.38
49 281474976710656 7036874417766.40
50 562949953421312 14073748835532.80
51 1125899906842620 28147497671065.60
52 2251799813685250 56294995342131.20
53 4503599627370500 112589990684262.00
54 9007199254740990 225179981368525.00
55 18014398509482000 450359962737050.00
56 36028797018964000 900719925474099.00
57 72057594037927900 1801439850948200.00
58 144115188075856000 3602879701896400.00
59 288230376151712000 7205759403792790.00
60 576460752303424000 14411518807585600.00
61 1152921504606850000 28823037615171200.00
62 2305843009213690000 57646075230342400.00
63 4611686018427390000 115292150460685000.00
64 9223372036854780000 230584300921369000.00 461168601842739000.00
Total 18446744073709600000 461168601842739000.00

This is assuming that each rice grain's weight is 0.025 grams which is a decently accurate guesstimation. The courtier requested 461168601842739000.00 grams of rice. What's the big deal, it is a quantifiable unit after all. But here are some interesting facts when you try to get a perspective of that quantity -

  1. If you end up stacking this many number of rice grains, it will be the size of mount everest. 
  2. If you end up weighing these many number of rice grain, it will be approximately 101 trillion pounds or 461 billion metric tons
  3. This requested rice quantity is around 1000 times more than the global rice production in 2010. 
This also brings us to another interesting idea. It is known as Second Half of the ChessBoard. If you look closely, you will realize that the first half of the chessboard requires a total quantity of rice to be around 100,000 kgs. Good enough? Well, India's annual rice output is 1,200,000 times that amount. But, by the time you reach 64th square that quantity of rice is 1000 times the global rice production. Isn't it mind boggling, the numbers added by the second half of the chess board. This is where an exponentially growing factor begins to have a significant impact.

Hence, the bottomline! Compounding in investing works on two basic premises - 
  1. The earnings have to be reinvested with the principal.
  2. The longer you wait, the more significant wealth you generate.
That is the power of compounding! Now, you know ...