For calculating my fixed rate mortgage, this is my excel equation, that I got from someone off the net:
=(((1+$D$4/2)^2)^(14/365)-1)*F128
$D$4 is my interest rate of 2.89%.
It's 2.89%/2 squared because it's compounded semi-annually.
F128 is the previous principal balance on which the current interest is calculated.
It's every two weeks, hence the 14/365.
So, (((1+0.0289/2)^2)^(14/365)-1)*(previous balance) = current interest amount.
If say the current principal balance is $300000, and the rate is 2.89%, and it's being paid every two weeks, then the interest amount is:
(((1+0.0289/2)^2)^(14/365)-1)*(300000) = $330.35
If your payment is say $1500, then the principal payment is $1169.55.
That means after the payment the remaining principal is $298830.45.
For the next pay period, the equation is (((1+0.0289/2)^2)^(14/365)-1)*(298830.45) = $329.06 interest.
I'm usually bang on, but occasionally, I'm off by 1¢, which is really annoying for my OCD personality.
Calculation worked with multiple different banks, although instead of the 14/365 for biweekly payments, I was using 1/12 for a monthly payment.
Try it and see if you get the same numbers.
All else being equal, what do you thinks is better? --
2.59% fixed for 3-years
2.89% fixed for 5-years
Depends on you. Where are you in the amortization? For example, if you're near the beginning, the 5-year may prove attractive for the extra 2-years of peace of mind but then again, it might not because you know you're paying 0.3% more. However, that's a heluvalot better than paying say 1.8% more for 10-year fixed vs a 5-year fixed. I know we have been saying this for years, but interest rates may really start to rise in the next year or so.
2.89% is an excellent 5-year fixed rate. 2.84% is possible, but if your existing lender is offering you 2.89%, then I'd take it, and avoid the extra fees and hassle involved with switching lenders.
BTW, when I called my bank for a renewal, they offered me 3.29%, and that was the lowest the phone rep could offer immediately. I said no thanks, because 2.89 - 2.99% were available to me elsewhere. The next day they approved 2.89%. IOW, all it took was some minor negotiation over the phone to get 0.4% chopped off their "best" rate. I guess they really like to start high with their rates for customers that are not as well informed.