Affordability is the extra free cash flow you can use to spend or invest.
We calculated based on this, [All Income p/m - All Expenses p/m - All Savings & Investments p/m = Affordability]
Sustainability is how long you can sustain if you lost your job/income.
We calculated based on this [Total cash on hand - All Expenses p/m - All Savings & Investments p/m = Sustainability]
* At this moment, not considering the FD, or Investment that you are able to withdraw as cash.