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.