it looks stupid.
i've tried many calculations to try to calculate the year. i thought that the year is kept in the memory of my RTC, but i was wrong, the yearbits (as said in the datasheets) were used for the leap year.

i thought that these 2 bits are used for the year. now i have made another variable "year" and wrote the variable to an EEPROM. and when i need to read the date, i first read the days/months from the RTC, and after that i read the year out of an EEPROM.

after fixing this, i only have to change some value's in my calculation to alter the time/date. now i can alter the time and date by using the arrows on my pc keyboard. the arrows left and right to select the "hours", "minutes", "seconds", "days",
"months" and "years". with the up and down arrows the variable increses or decreses by 1.