4chan

Felt like nerding out on this.

You can use the rule of 72 to figure compounding inflation (or interest) in your head. Just take 72 divided by your inflation rate and you get how long it takes for a price to double. Example: Assuming 3% yearly inflation , It would take 72/3 or 24 years for the price to double. Then, just double the starting price for each 24 year period. So assuming a car was 1,000 in 1950, it would cost about 2,000 in 1975, 4,000 in 2000, and 8,000 in 2025 if inflation for that product was exactly 3% yearly.

A couple percentage points difference makes a huge difference in how long it takes for a price (or investment to grow). The stock market has an average yearly interest rate of like 8%. That translates into a investment portfolio doubling every 9 years instead of the 24 years it would be for 3%. So 45 years in the market would turn an initial 1k investment into a ~$32k investment.

Of course, you could also use an online compound interest calculator(simple one here), but I like to know how to do the calculation myself personally.