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Hopefully someone can help me with a formula that appears to be reasonably simple to figure out, for any experienced HP user. I'm just not all that savvy when it comes to creating formulas.

Anyone familiar with the HP 19B calculator probably knows the formula below is the one used to solve for Present Value and loan calculations in leasing and loans.

ADV:PMT=(-PV-FV*(SPPV(I%YR/12:N)))/(USPV(I%YR/12:N-#ADV)+#ADV)

My goal is to simply add one simple step to the formula (or create another one if need be) to add "Annual Debt Service (ADS)calculation. In other words, once a payment is caluclated, I'd like to be able to have the calculator compute the payment AND multply by 12, which equals the ADS (Annual Debt Servive). This is a common component in real estate investment comparisions when analyzing the projected cash flow.

Thank you for your assistance.

Barry

Barry:

Probably the easiest way is just to multiply by 12 to get ADS after you've calculated PMT. BUT you can save *2* keystrokes, i.e. RCL PMT, instead of *,1,2,= by using the following formula, solving for ADS, and recalling the PMT ;-)


ADV:12*L(PMT:(-PV-FV*(SPPV(I%YR/12:N)))/(USPV(I%YR/12:N-#ADV)+#ADV))-ADS+0*PMT


Bob

Barry:


I thought a little more about your request, and here are 3 approaches. The first one is probably what you are looking for, but it comes with a BIG CAVEAT. You ABSOLUTELY, POSITIVELY MUST solve for PMT first, before pressing ADS. Otherwise, the ADS you get will be based on the old value stored in PMT. The other 2 alternatives will alert you with an error message:

Option 1: Enter all values, press MORE, PMT, *THEN* ADS:


ADV:IF(S(PMT):(-PV-FV*(SPPV(I%YR/12:N)))/(USPV(I%YR/12:N-#ADV)+#ADV)-PMT:12*PMT-ADS)

Option 2: Enter all values, press MORE, ADS, RCL PMT:


ADV:12*L(PMT:(-PV-FV*(SPPV(I%YR/12:N)))/(USPV(I%YR/12:N-#ADV)+#ADV))-ADS+0*PMT

Option 3: Enter all values, press MORE, PMT, RCL ADS:


ADV:L(ADS:12*(-PV-FV*(SPPV(I%YR/12:N)))/(USPV(I%YR/12:N-#ADV)+#ADV))/12-PMT+0*ADS


Hope this helps,

Bob