Custom Incremental Fine Structures in Koha Library System

Step-by-step breakdown of how Koha calculates incremental fines for overdue items, especially with a tiered/incremental fine logic like the one used in your custom CalcFine function:

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✅ Step-by-Step Custom Incremental Fine Structures in Koha Library System

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1. Check if the Item is Overdue

return (0, 0, 0) unless (DateTime->compare($due_dt, $end_date) == -1);

• If the item is not overdue, no fine is charged.

• DateTime->compare() checks if the return date is later than the due date.

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2. Determine the Item Type and Fetch Circulation Rules

$itemtype = $item->{itemtype} || $item->{itype};
$issuing_rule = Koha::CirculationRules->get_effective_rules(...);

• This pulls the rules like:

  • fine

  • chargeperiod

  • firstremind (grace period)

  • overduefinescap

  • recall_overdue_fine

  • cap_fine_to_replacement_price

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3. Calculate Overdue Time (in units: days/hours)

my $chargeable_units = get_chargeable_units($fine_unit, $start_date, $end_date, $branchcode);
my $units_minus_grace = $chargeable_units - ($issuing_rule->{firstremind} || 0);

• get_chargeable_units() calculates total overdue time.

• firstremind is subtracted if FinesIncludeGracePeriod is disabled.

• If units_minus_grace is zero or negative → No fine.

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4. Determine How Many Fine Periods Apply

my $charge_periods = $units / $issuing_rule->{chargeperiod};
$charge_periods = ceil(...) or floor(...) based on `chargeperiod_charge_at`

• Example: 20 days overdue, chargeperiod = 1 → 20 charge periods.

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5. Check for Recalls (Optional Path)

if (recall exists and issuing_rule->{recall_overdue_fine}) {
    $amount = $charge_periods * recall_overdue_fine;
}

• If the item or biblio is recalled and recall_overdue_fine is set, use this amount per unit.

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6. Apply Custom Incremental Fine Formula

If no recall, calculate based on custom tiered rate:

if ($charge_periods <= 15) {
    $amount = $charge_periods * 1;
} elsif ($charge_periods > 15 && $charge_periods <= 30) {
    $amount = 15 + ($charge_periods - 15) * 2;
} else {
    $amount = 45 + ($charge_periods - 30) * 5;
}

🔢 Breakdown of Formula:

• Day 1–15 → ₹1/day → 15

• Day 16–30 → ₹2/day → 15 * 1 + 15 * 2 = ₹45

• Day 31+ → ₹5/day → 45 + (extra days * 5)

Example:

• 40 overdue days →
  15*1 + 15*2 + 10*5 = ₹15 + ₹30 + ₹50 = ₹95

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7. Apply Overdue Cap (if any)

if ($amount > $issuing_rule->{overduefinescap}) {
    $amount = $issuing_rule->{overduefinescap};
}

• Maximum fine allowed per rule.

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8. Apply Replacement Price Cap (if allowed)

if ($issuing_rule->{cap_fine_to_replacement_price} && $amount > $item->{replacementprice}) {
    $amount = $item->{replacementprice};
}

• This prevents fine from exceeding the item's value.

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✅ Return Values

return ($amount, $units_minus_grace, $chargeable_units);

• Final fine amount

• Effective overdue units (after grace)

• Total overdue time (raw)

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💡 Summary Table (Incremental Fine Logic)

Days Overdue	Rate per Day	Cumulative Fine
1–15	₹1	15 * 1 = ₹15
16–30	₹2	₹15 + 15 * 2 = ₹45
31+	₹5	₹45 + (days - 30) * 5

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Would you like this logic formatted for configuration as a policy document or admin guide for library staff?

Koha Incremental Fine Calculation Formula

Step-by-Step Overview

1. Check if the item is overdue:
   If the return date is after the due date, continue.
2. Determine overdue days:
   Overdue Days = Return Date - Due Date
3. Apply Grace Period:
   Chargeable Days = Overdue Days - First Reminder (grace days)
4. Calculate Fine Based on Tiers:
   • Days 1–15: ₹1 per day
   • Days 16–30: ₹2 per day
   • Days 31+: ₹5 per day
5. Apply Fine Caps:
   • If fine > overduefinescap, cap to overduefinescap
   • If enabled, also cap fine to item's replacementprice

Fine Tier Breakdown

Days Overdue	Rate per Day	Cumulative Fine
1–15	₹1	Up to ₹15
16–30	₹2	₹15 + (days - 15) × ₹2
31+	₹5	₹45 + (days - 30) × ₹5

* This stepped fine model is a custom enhancement and may differ from Koha's default flat-rate fines.