Why one-at-a-time beats spreading it around
The instinct is to split extra money across all debts evenly. The maths disagrees: interest compounds per balance, so concentrating fire kills one interest stream entirely, then rolls that debt's freed-up minimum into the next attack, the payments cascade. Both strategies above use this structure; they differ only in target order.
What the two orderings optimise
| Snowball (smallest balance first) | Avalanche (highest rate first) | |
|---|---|---|
| Optimises | Number of debts cleared early | Total interest paid |
| First win arrives | Fast | Depends on where the high-rate balance sits |
| Best when | Motivation is the binding constraint | Rates differ a lot across debts |
The research on debt behaviour consistently finds completion matters more than optimality, people who see early wins finish their plans more often. That is a real effect, not weakness; a plan you finish at slightly higher interest beats an optimal plan you abandon in month seven. The calculator prints both totals so the price of the motivating order is a known number rather than a fear.
Making the plan survive contact with reality
- Stop the refill. A payoff plan with active card spending is a treadmill. Freeze or remove the cleared cards from daily carry, closing them is optional (it can affect credit utilisation), but not using them is mandatory.
- Automate the attack payment the day after payday. Money that waits for month-end gets spent.
- Negotiate rates first. A single call asking a card issuer for a lower APR succeeds surprisingly often, and every point conceded shortens the plan for free.
- Windfalls go to the target debt, not spread thin. The cascade does the rest.
After the last debt
The attack payment you have been making is now free cash flow your budget already survives without. Redirecting it straight into an emergency fund and then compounding investments converts the discipline you built into wealth at the same monthly cost. People who route it back into lifestyle rebuild the debts; people who redirect it retire the pattern along with the balances. If a mortgage remains, the early payoff calculator shows what the same habit does there.