Payback Period

The time it takes for the gains from an investment to recover its cost.

Example

A 6,000 course that adds 4,200 a year after tax pays back in about 1.4 years.

It ignores what happens after payback and the time value of money, so use it as a quick filter rather than a full valuation.

Return on investment (ROI) — Total proceeds less total cost, divided by total cost - the simplest measure of what an investment produced.
Opportunity cost — What you give up by choosing one use of your money, or time, over the next-best alternative.

The return is the earnings difference, not the certificate — A self-investment pays off through higher earnings, better opportunities or more working years. Measure it as a difference over time, after tax, against what it cost. (11 min)
The real price includes the income you give up and the years the skill stays valuable — A self-investment's full cost is fees plus lost earnings plus time. Its value depends on how large the earnings difference is and how long it lasts before the skill ages. (12 min)
Appraising one opportunity: evidence of the outcome, not the promise of it — Before paying for a course, qualification or programme, look for evidence that people like you achieved the outcome you want, check completion and employer demand, and compare cheaper routes. (12 min)
Borrowing for skills that may not pay, and tax relief that depends on where you live — The biggest risks are paying for education that does not change earnings, financing it with debt, and skills losing value. Tax treatment of education costs and support varies by country. (11 min)