The Rule of 10’s
This is used to determine the future value of money. For every 10 years in the future you will need double the income to keep your current standard of living.
e.g. You want to retire with R20,000 per month in 30 years.
In 10 years you will need R40,000 per month (R20,000×2)
In 20 years you will need R80,000 per month (R40,000×2)
In 30 years you will need R160,000 per month (R80,000×2)