Sri Lanka Debt Payoff Calculator, Snowball vs Avalanche

The calculator runs a month-by-month simulation of your debts using the reducing-balance (monthly-compounding) method, the same basis Sri Lankan banks and finance companies use to quote effective interest, and the same engine behind this site's EMI calculator. No opinion or assumption is added: every figure comes only from the balances, rates, and minimums you enter.

Each debt i has a balance Bᵢ, a monthly rate rᵢ = APRᵢ ÷ 12 ÷ 100, and a minimum mᵢ. Your total budget is P, and the extra above the minimums is E = P − Σmᵢ, recomputed as debts clear. Every month the engine:

1. Adds interest to each open debt: Bᵢ ← Bᵢ + Bᵢ·rᵢ.
2. Pays every open debt its minimum, capped at the balance.
3. Pours the remaining budget into one target debt, the smallest balance under snowball, or the highest rate under avalanche.
4. When a debt clears, its freed minimum plus any overshoot rolls straight into the next target that same month, the snowball effect.
5. Repeats until every balance reaches zero, tallying interest along the way.

The two strategies differ in one thing only, step 3's ordering, so the interest gap between them is a clean, objective result, not a guess. Avalanche targets your priciest rate first and therefore always pays the least total interest; snowball clears a whole debt sooner for an early psychological win. To keep the engine honest, single-debt cases are cross-checked against the closed-form amortization formula n = ⌈ln(P ÷ (P − rB)) ÷ ln(1 + r)⌉, which agrees to the rupee. A debt whose minimum does not exceed its own monthly interest can never shrink, so the tool flags it before you get a misleading answer.

Every figure above is produced by the same engine that powers the calculator, reconciled so that, for each debt, total paid = starting balance + interest (Example 2 avalanche: Rs 190,021 paid on Rs 160,000 of principal; snowball costs Rs 4,810 more interest).

• Central Bank of Sri Lanka: Interest Rates statistical tables (indicative APR bands)
• Central Bank of Sri Lanka: official site (directions on credit card advances)
• Reducing-balance / compound-interest amortization: methodology reference

The calculation engine and indicative rate bands were last cross-checked on 2026-07-11. The reducing-balance method and the closed-form amortization cross-check are standard and do not change; the indicative rate chips are reviewed against Central Bank rate bulletins. You always enter your own actual rates, nothing here is assumed for you.