The answer is 40.

 

Not 40 thousand.  Just 40.  This is because of the power of compounding and exponential growth over time.

 

Here is the proof:

How many doubles	Millimeter	KM
0	0.5	0.0000005
1	1	0.000001
2	2	0.000002
3	4	0.000004
4	8	0.000008
5	16	0.000016
6	32	0.000032
7	64	0.000064
8	128	0.000128
9	256	0.000256
10	512	0.000512
11	1024	0.001024
12	2048	0.002048
13	4096	0.004096
14	8192	0.008192
15	16384	0.016384
16	32768	0.032768
17	65536	0.065536
18	131072	0.131072
19	262144	0.262144
20	524288	0.524288
21	1048576	1.048576
22	2097152	2.097152
23	4194304	4.194304
24	8388608	8.388608
25	16777216	16.777216
26	33554432	33.554432
27	67108864	67.108864
28	134217728	134.21773
29	268435456	268.43546
30	536870912	536.87091
31	1073741824	1073.7418
32	2147483648	2147.4836
33	4294967296	4294.9673
34	8589934592	8589.9346
35	17179869184	17179.869
36	34359738368	34359.738
37	68719476736	68719.477
38	1.37439E+11	137438.95
39	2.74878E+11	274877.91
40	5.49756E+11	549755.81

Evolution has left us with a brain that is quite good at guestimating small liner maths – but sometimes it can be a struggle when it comes to a formula that includes ^ (to the power of).

So when you see something growing at 7% or 10% p.a. you might think this is not a big difference.  Over 40 years it can be huge.

If you had $100,000 in super and it grew at 10% not 7% for 30 years, you would have $1,700,000 rather than $760,000.  Almost a million dollars better off.

Big differences can result from such a small change in return and starting your journey with 20 years to retirement rather than 5.