PHP calculates personal income tax

Preface

Before using this calculation , You need to know the total amount of tax paid in that year and the amount of tax payable in this month . These two parameters need to be calculated according to their respective system data , This method only implements the individual income tax calculation algorithm . Besides , Need to open PHP Of bc Expand .

Parameters

Method passes in two parameters , The taxable amount of the current month as well as The total amount of tax paid this year （ Excluding the current month ）.

• $lauwen_monthly_tax_amount： The taxable amount of the current month .
• $lauwen_taxed_amount： The total amount of tax paid in that year （ Excluding the current month ）.

Realization

The first is to confirm two levels , One is the tax rate level of the total amount of tax paid this year （ Excluding the current month ）, The other is the tax rate level of the total amount of tax paid this year after this month （ Including current month ）; Finally, two calculation methods are used in the calculation of individual income tax , One is to calculate the tax at each tax rate level separately ; The other is to use quick calculation deduction to calculate , Just use it as needed .

Hierarchical computing core code

    //  Calculation by grading method 
    $tax = '0';
    while ($new_key >= $old_key) {
        $level_amount = bcsub($lauwen_month_after_amount, $lauwen_tax_amounts[$new_key], 6);
        if ($new_key == $old_key) {
            $level_amount = bcsub($lauwen_month_after_amount, $lauwen_taxed_amount, 6);
        }

        $tax = bcadd($tax, bcmul($level_amount, $lauwen_tax_rates[$new_key]), 2);

        $lauwen_month_after_amount = $lauwen_tax_amounts[$new_key];
        $new_key --;
    }

Quick calculation deduction calculation core code

    //  Quick calculation deduction method 
    $quickly_old_tax = bcsub(bcmul($lauwen_taxed_amount, $lauwen_tax_rates[$old_key], 6), $lauwen_tax_quickly[$old_key], 6);
    $quickly_new_tax = bcsub(bcmul($lauwen_month_after_amount, $lauwen_tax_rates[$new_key], 6), $lauwen_tax_quickly[$new_key], 6);
    $tax0 = bcsub($quickly_new_tax, $quickly_old_tax, 2);

All the code

function personTax($lauwen_monthly_tax_amount, $lauwen_taxed_amount) {
    $lauwen_tax_amounts = ['0', '36000', '144000', '300000', '420000', '660000', '960000'];
    $lauwen_tax_rates = ['0.03', '0.1', '0.2', '0.25', '0.3', '0.35', '0.45'];
    $lauwen_tax_quickly = ['0', '2520', '16920', '31920', '52920', '85920', '181920'];

    $lauwen_taxed_amount = (string)$lauwen_taxed_amount;
    $lauwen_monthly_tax_amount = (string)$lauwen_monthly_tax_amount;
    $lauwen_month_after_amount = bcadd($lauwen_taxed_amount, $lauwen_monthly_tax_amount, 6);

    //  Determine the level of the total amount of tax paid in the current year before the current month , And the level of the total amount of tax paid in the current year after the current month 
    $old_key = 0;           //  Level before the month 
    $new_key = 0;           //  Level after the month 
    $end_key = count($lauwen_tax_amounts) - 1;
    foreach ($lauwen_tax_amounts as $key => $val) {
        if ($key == $end_key) {             //  The last level 
            if (bccomp($lauwen_taxed_amount, $val, 2) == 1) {
                $old_key = $key;
            }

            if (bccomp($lauwen_month_after_amount, $val, 2) == 1) {
                $new_key = $key;
            }
        } else {            //
            if (bccomp($lauwen_taxed_amount, $val, 2) == 1 && bccomp($lauwen_taxed_amount, $lauwen_tax_amounts[$key+1], 2) == -1) {
                $old_key = $key;
            }

            if (bccomp($lauwen_month_after_amount, $val, 2) == 1 && bccomp($lauwen_month_after_amount, $lauwen_tax_amounts[$key+1], 2) == -1) {
                $new_key = $key;
                break;
            }
        }
    }

    //  Quick calculation deduction method 
    $quickly_old_tax = bcsub(bcmul($lauwen_taxed_amount, $lauwen_tax_rates[$old_key], 6), $lauwen_tax_quickly[$old_key], 6);
    $quickly_new_tax = bcsub(bcmul($lauwen_month_after_amount, $lauwen_tax_rates[$new_key], 6), $lauwen_tax_quickly[$new_key], 6);
    $tax0 = bcsub($quickly_new_tax, $quickly_old_tax, 2);

    //  The difference method 
    $tax = '0';
    while ($new_key >= $old_key) {
        $level_amount = bcsub($lauwen_month_after_amount, $lauwen_tax_amounts[$new_key], 6);
        if ($new_key == $old_key) {
            $level_amount = bcsub($lauwen_month_after_amount, $lauwen_taxed_amount, 6);
        }

        $tax = bcadd($tax, bcmul($level_amount, $lauwen_tax_rates[$new_key]), 2);

        $lauwen_month_after_amount = $lauwen_tax_amounts[$new_key];
        $new_key --;
    }

   return json_encode([
       "normal"     =>  $tax,
       "quickly"    =>  $tax0,
   ]);
}