Debt Freedom Date Calculator

This calculator projects a month-by-month payoff of Total Debt Balance at Average Interest Rate under Monthly Payment, running the loop for up to 600 months (50 years) before giving up (line 78). Monthly Payment dominates Months to Debt Freedom: its ±10% span is about 26% of Months to Debt Freedom — more than Total Debt Balance (about 23%) or Average Interest Rate (a much smaller ~3%) — because a bigger payment shortens the payoff loop directly while the rate only changes how much of each payment goes to interest versus principal. Before the simulation runs, the engine checks whether Monthly Payment can even cover a month's interest on Total Debt Balance (line 61): if Monthly Payment is at or below Total Debt Balance times Average Interest Rate divided by 12, both Months to Debt Freedom and Payoff Date return the literal sentinel value -1 instead of a real month count, because the balance would never actually shrink at that payment. At this calculator's own defaults, that exact floor is $260.4166...67 a month (the displayed $800 default clears it comfortably). There are two distinct, and differently dangerous, failure modes around that floor.

At or below the exact floor, both outputs cleanly flip to the -1 sentinel. But just above it — even a fraction of a cent above, including at a nominal $260.42, which is only about half a cent over the true floor — no sentinel fires at all: the simulation runs the full 600-month loop and reports ordinary-looking numbers (Months to Debt Freedom of 600, Total Interest Paid of roughly $156,092) while the balance has barely budged, still sitting around $24,840 of the original $25,000 after 50 years. That second failure mode is silent and arguably worse than the -1 case, because it looks like a normal, if slow, payoff rather than a mathematically near-impossible one. This calculator does not account for changing interest rates, extra lump-sum payments, or new debt added after the projection starts.