Date algorithm.


Hi, everybody!

I wonder if sometime "hp" publishes her algorithm to calculate the date, by given date and number of days?

Any other algorithm appreciated also.

Best regards, Tal email:


As far as I know, that means up to the 41 series, HP always published their formulas agorithm. I remember I saw the date calculation algorithm on the manual of the HP 1C ans on an application pac for the 34C.

I'll try to find it for you.

Best regards,



For a simple version, see the HP25 Applications Manual; and for a more elaborated version, the HP41 Standard Pac manual (it comes with the calculator, the ROM module was an option).


It's also in the 12C manual, appendix D. I've "borrowed" it a couple of times to stick in various programs that I've built over the years because it's so simple and easy to implement.

here it is:

delta-days = f(d1)-f(d2)

dn = 365(yyyy) + 31(mm-1) + dd + INT(z/4) - x where :

if mm<=2 x=0; z=(yyyy)-1

else x=INT(0.4mm + 2.3); z=(yyyy)

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