See if your withdrawal amount is safe, or how many months your savings will last.
Simulates the corpus month by month: it earns a return, then the withdrawal is deducted.
If withdrawals consistently exceed what returns replace, the corpus eventually reaches zero.
Each month: Balance × (1 + monthly rate) − withdrawal
What does 'sustainable' mean here?
It means the returns on your savings are enough to cover your withdrawals, without your balance running out over time.