Most accurate auction tontine payout formula (with interest)
Step-by-step auction tontine math: live slot and dead slot contributions, net take-home, organizer commission, multi-period table, FAQ, and a period checklist.
Running an auction tontine (interest-bearing hụi) demands precise math to protect both the organizer and every member. One wrong period total can throw the whole chain off by tens of millions of đồng. This guide is the standard way to calculate auction tontine money: live slot / dead slot formulas, net take-home, organizer commission, a worked multi-period table, and a checklist that prevents silent spreadsheet drift.
Prefer not to crunch numbers by hand? Use the free Excel tontine ledger or automate everything in the Huio app.
1. What are live slots and dead slots?
Before you apply any formula, lock these two core auction-tontine concepts:
- Live slot: a member who has not yet taken the pot. In the current period, each live slot pays face value minus the winning bid (the auction interest for that draw).
- Dead slot: a member who already took the pot in an earlier period. They pay the full face value, with no interest deduction.
One person may hold several slots in the same chain—some live, some dead. Always calculate per slot, never “per person name.” Merging slots by nickname is the most common reason a hand-built Excel file goes sideways.
Read more: What are live slots and dead slots?.
2. Variables you need before calculating
| Variable | Meaning | Example |
|---|---|---|
| (N) | Total slots / total periods | 10 |
| (G) | Face value (base contribution per slot per period) | 2,000,000 VND |
| (B) | Winning bid (interest) for the current period | 300,000 VND |
| (D) | Dead slots before the current period | 2 |
| (S) | Remaining live slots (excluding the winner this period) | (N - D - 1) |
| (H) | Organizer commission / tiền thảo (by agreement) | 1,000,000 VND |
Period convention: period 1 is usually the opening draw; the dead-slot count rises each time someone successfully takes the pot.
3. Formula for the actual take-home amount
In any draw period:
Net take-home = Live-slot collections + Dead-slot collections − Organizer commission
Where:
- Each live slot pays = (G - B)
- Live-slot total = (S \times (G - B))
- Each dead slot pays = (G)
- Dead-slot total = (D \times G)
- Commission (H) = by agreement (fixed / half-share / % of the pot…). See how to calculate organizer commission.
Quick check formula
[ \text{Take-home} = S(G - B) + DG - H ]
If the result is negative or “unreasonably low” (for example, far below face value near the end of the chain without a clear reason), stop and re-check (S), (D), and (B).
4. Detailed worked example (period 3)
Assume a monthly chain with:
- Slots (N = 10) (10 periods)
- Face value (G = 2{,}000{,}000) VND per slot per period
- Organizer commission (H = 1{,}000{,}000) VND (deducted from each take-home—the common model)
- In period 3, Mr. A wins with (B = 300{,}000) VND
At period 3:
- There are already 2 dead slots from periods 1–2 → (D = 2)
- Mr. A is the winner this period → he is not counted as a live payer
- Remaining live slots: (S = 10 - 2 - 1 = 7)
Amounts due by group
| Group | Slots | Per-slot due | Total |
|---|---|---|---|
| Live slots | 7 | 2,000,000 − 300,000 = 1,700,000 | 11,900,000 |
| Dead slots | 2 | 2,000,000 | 4,000,000 |
| Gross collected | 15,900,000 |
What Mr. A actually receives
[ 15{,}900{,}000 - 1{,}000{,}000\ (\text{commission}) = \mathbf{14{,}900{,}000\ \text{VND}} ]
From period 4 onward, Mr. A’s slot is dead.
5. Multi-period simulation table (for ledger cross-checks)
Assume winning bids (illustrative): period 1 = 0 VND (lottery / no interest), period 2 = 200,000 VND, period 3 = 300,000 VND, period 4 = 250,000 VND. Commission fixed at 1,000,000 VND each take-home.
| Period | Bid (B) | (D) | (S) | Live pays | Dead pays | Gross | Net after commission |
|---|---|---|---|---|---|---|---|
| 1 | 0 | 0 | 9 | 2,000,000 | — | 18,000,000 | 17,000,000 |
| 2 | 200,000 | 1 | 8 | 1,800,000 | 2,000,000 | 16,400,000 | 15,400,000 |
| 3 | 300,000 | 2 | 7 | 1,700,000 | 2,000,000 | 15,900,000 | 14,900,000 |
| 4 | 250,000 | 3 | 6 | 1,750,000 | 2,000,000 | 16,500,000 | 15,500,000 |
Copy this table into Excel and compare against the free tontine ledger template.
6. Common calculation mistakes (and how to avoid them)
6.1. Miscounting live vs dead slots
The #1 error: treating the current winner as still live, or forgetting to exclude the winner from (S).
Rule: In period (k), the winner is not in (S); (D) only includes people who took the pot before period (k).
6.2. One person, many slots
If Sister B has two live slots and one dead slot in the same period, the ledger needs three lines. Bundling everything as “Sister B pays X” invites disputes.
6.3. Short payments, late payments, partial payments
The formulas above are amounts due under the chain rules. Amounts actually received can differ. A professional ledger needs two columns: due and received (partial payment). Dedicated tontine apps track both states separately.
6.4. Taking commission at the wrong moment
Some chains deduct commission from the take-home; others add it into every period’s contribution. Changing models mid-chain without a signed addendum destroys reconciliation. Agree at period 1 and stick to it.
6.5. Interest outside the legal frame
Interest-bearing tontines must stay within the framework in Decree 19/2019/NĐ-CP. Excess interest may be unenforceable in a dispute.
7. Organizer checklist before every draw
- Confirm the live / dead slot list is updated after the previous period.
- Record the winning bid and the winner (with supporting evidence if available).
- Compute (G - B) for live slots; (G) for dead slots.
- Deduct or add organizer commission using the agreed model.
- Issue per-member debt notices before the due date.
- Reconcile: total collected = sum of slot dues ± adjustments (if any).
- Keep receipts / VietQR bank statements.
8. FAQ — common auction tontine math questions
Does the last period still need an auction?
Depends on the chain rules. Many chains let the last remaining slot take the residual with (B = 0), or with another agreed rule. The same formula still works once (B) and (H) are defined.
Should we round amounts?
Yes—agree up front to round to 1,000 VND or 10,000 VND and apply it consistently. Never round “by feel” period to period.
Do weekly / daily tontines use a different formula?
Same formula; the cycle length and operational risk differ (more frequent dunning). See daily / weekly / monthly tontine types.
Is Excel enough?
Enough for one or two small chains if you are disciplined with formulas. With many chains or many slots per person, cell drift and lost files become expensive—see free Excel tontine ledger.
9. Automate with Huio
Hand-calculating dozens of chains invites errors—especially with short pays or mid-period slot transfers. Huio calculates on a slot-centric model: when you lock an auction, the system splits live / dead / commission, creates notices, and helps chase overdue balances.
- Create a chain & auction rules: Help — Getting started
- Calculation rules: Help — Calculations & periods
- Download: huio.app
A correct formula only matters when the ledger is recorded the same way every period. Choose a tool that lets you—and your members—see one shared number.