var personal, A1, A2, A3, B1, B2, B3;
var inctax, res1, res2, res3, lev1, lev2, lev3, taxdue; 

function calculate(year,income,tax){
    year = document.forms['oblicz'].year.value;
    income= document.forms['oblicz'].income.value;
    tax=document.forms['oblicz'].tax.value;
    
    if(year=='0')
    {document.forms['oblicz'].zwrot.value = '';
    }
    else{if(income==''){document.forms['oblicz'].zwrot.value = '';}
        else{if(tax==''){document.forms['oblicz'].zwrot.value = '';}
            else{switch(eval(year)){
                     case 2011:personal = 6475; A1 = 0;A2 = 37400;A3 = 0;B1 = 0;B2 = 0.2;B3 = 0.4;break;
                    case 2010:personal = 6475; A1 = 0;A2 = 37400;A3 = 0;B1 = 0;B2 = 0.2;B3 = 0.4;break; 
                    case 2009:personal = 6035;A1 = 0;A2 = 34800;A3 = 0;B1 = 0;B2 = 0.2;B3 = 0.4;break;
                    case 2008:personal = 5225;A1 = 2230;A2 = 34600;A3 = 0;B1 = 0.1;B2 = 0.22;B3 = 0.4;break;
                    case 2007:personal = 5035;A1 = 2150;A2 = 33300;A3 = 0;B1 = 0.1;B2 = 0.22;B3 = 0.4;break;
                    case 2006:personal = 4895;A1 = 2090;A2 = 32400;A3 = 0;B1 = 0.1;B2 = 0.22;B3 = 0.4;}
            
             
        inctax = Math.max((income - personal), 0);
        res1 = Math.min(inctax, A1);
        lev1 = res1 * B1;res2 = Math.min((inctax - res1), A2);
        lev2 = res2 * B2;res3 = Math.max((inctax - res2 - res1), A3);
        lev3 = res3 * B3;
        taxdue = lev1 + lev2 + lev3;
        document.forms['oblicz'].zwrot.value = Math.round(tax - taxdue);}}}     
    }