Developing a project cost calculator using 1C-Bitrix

Project Cost Calculator Development for 1C-Bitrix

A project cost calculator is a primary qualification tool for IT companies, agencies, project organisations and studios. It does not give an exact price — that is impossible without delving into the task — but it helps the client understand the order of magnitude and segments incoming enquiries: it filters out non-target requests and warms up serious ones.

Specifics of Project Work Calculation

A project is not a product with a fixed price. The cost depends on:

• The set of functional blocks (what is included in scope)
• The complexity of each block (from standard to custom)
• The technology stack (development speed, licence costs)
• Deadlines (an urgent project costs more)
• Relationship type (one-off development, support, outsourcing)

The calculator structures these variables into a manageable questionnaire.

Data Model: Blocks and Their Costs

Functional blocks are stored in a HighLoad block ProjectBlocks:

PHP Calculator with Dependency Resolution

namespace MyProject\Services\Calculators;

class ProjectCostCalculator
{
    private array $blocks;
    private array $selectedIds;
    private float $urgencyCoeff;
    private float $marginPercent;

    public function __construct(
        array $allBlocks,
        array $selectedIds,
        string $urgency = 'normal',
        float $marginPercent = 30
    ) {
        $this->blocks       = $allBlocks;
        $this->selectedIds  = $this->resolveDependencies($selectedIds, $allBlocks);
        $this->urgencyCoeff = match ($urgency) {
            'urgent'   => 1.5,
            'fast'     => 1.25,
            'normal'   => 1.0,
            'flexible' => 0.9,
            default    => 1.0,
        };
        $this->marginPercent = $marginPercent;
    }

    public function calculate(): array
    {
        $breakdown    = [];
        $totalHoursMin = 0;
        $totalHoursMax = 0;
        $totalCost     = 0;

        foreach ($this->selectedIds as $blockId) {
            $block = $this->findBlock($blockId);
            if (!$block) continue;

            $hoursMin = $block['UF_HOURS_MIN'];
            $hoursMax = $block['UF_HOURS_MAX'];
            $rate     = $block['UF_HOURLY_RATE'];

            $costMin = $hoursMin * $rate * $this->urgencyCoeff;
            $costMax = $hoursMax * $rate * $this->urgencyCoeff;

            $totalHoursMin += $hoursMin;
            $totalHoursMax += $hoursMax;
            $totalCost     += ($costMin + $costMax) / 2;

            $breakdown[] = [
                'id'       => $blockId,
                'name'     => $block['UF_BLOCK_NAME'],
                'category' => $block['UF_CATEGORY'],
                'hours'    => "{$hoursMin}–{$hoursMax}",
                'cost_min' => round($costMin),
                'cost_max' => round($costMax),
            ];
        }

        // Add margin
        $margin    = $totalCost * ($this->marginPercent / 100);
        $finalCost = $totalCost + $margin;

        return [
            'breakdown'      => $breakdown,
            'hours_min'      => $totalHoursMin,
            'hours_max'      => $totalHoursMax,
            'cost_min'       => round($finalCost * 0.85),
            'cost_max'       => round($finalCost * 1.2),
            'cost_avg'       => round($finalCost),
            'urgency_coeff'  => $this->urgencyCoeff,
            'weeks_min'      => ceil($totalHoursMin / 40),
            'weeks_max'      => ceil($totalHoursMax / 40),
        ];
    }

    private function resolveDependencies(array $selectedIds, array $blocks): array
    {
        $resolved = $selectedIds;
        foreach ($blocks as $block) {
            if (in_array($block['ID'], $selectedIds, true) && !empty($block['UF_DEPENDS_ON'])) {
                $depId = (int)$block['UF_DEPENDS_ON'];
                if (!in_array($depId, $resolved, true)) {
                    $resolved[] = $depId;
                }
            }
            // Required blocks are always included
            if ($block['UF_IS_REQUIRED'] && !in_array($block['ID'], $resolved, true)) {
                $resolved[] = $block['ID'];
            }
        }
        return array_unique($resolved);
    }
}

UX: Checkboxes with Hints

The calculator interface is a set of groups with checkboxes. Each checkbox is accompanied by a brief description: the client understands what is included in the block.

// Update total on every change
document.querySelectorAll('.block-checkbox').forEach(cb => {
    cb.addEventListener('change', async () => {
        const selected = [...document.querySelectorAll('.block-checkbox:checked')]
            .map(el => parseInt(el.value));

        const urgency = document.querySelector('[name="urgency"]:checked').value;

        const resp = await fetch('/ajax/calculator/project/', {
            method: 'POST',
            body: new URLSearchParams({
                selected: JSON.stringify(selected),
                urgency,
                sessid: BX.bitrix_sessid(),
            }),
        });

        const data = await resp.json();
        updateResultPanel(data);
    });
});

Passing the Brief to CRM

The calculation result forms a structured brief:

// Create a deal in Bitrix24 or a lead in the site CRM
$comments = "PROJECT COST ESTIMATE\n\n";
$comments .= "Selected blocks:\n";
foreach ($calcResult['breakdown'] as $item) {
    $comments .= "— {$item['category']}: {$item['name']} ({$item['hours']} h.)\n";
}
$comments .= "\nTotal: {$calcResult['cost_min']} – {$calcResult['cost_max']}\n";
$comments .= "Timeline: {$calcResult['weeks_min']} – {$calcResult['weeks_max']} weeks\n";
$comments .= "Urgency: {$urgency}\n";

Development Timelines

The key rule: a project cost calculator must never give a price lower than the real one. It is better to add a 20–30% buffer and explain it as a "preliminary estimate" than to get a client with inflated expectations.