<prompt> Human: Ill try to explain. I have about 138,000 left on my home. I originally had a FHA 30 year mortgage at about 5.25 and am nearly done with my refi to a 15 year conventional at 2.87. I have nearly 50k in a standard savings account just sitting there. Currently my mortgage with PMI, insurance, taxes and all the trimmings is about 1100 per month. After the refi, apples to apples, it will be about 1135 per month. Not bad at all. So on top of that, I want to get hyper aggressive on paying this thing off. I dont want a mortgage anymore. This is the last real big debt I have and I want it gone so bad I can taste it. SO. We are trying to figure out how to get it paid off as quick as possible. I figured Id just wait until there was about 50k left on the principal and then just write and check and be done with it or just plunk it all down now and make payments. But when I started using calculators, the math says its better to take that 50k and pump it into the mortgage little by little every month instead of all at once. Why? Heres my math:Here are the diagrams. Maybe some of you could explain the math and why it works out this way.Scenario 1: Standard payments, no extra. Payoff date exactly 15 years.Scenario 2: Make one giant payment of 50k on Jan 1 2017 and normal payments until paid off. Paid off in 8 years 11 months. Interest savings of 19,699.Scenario 3: Take 50k and spread it out over 4 years which is an extra 1041 per month. Paid off in 6 years 5 months. Interest savings of 18,891.31 It seems like voodoo to me. Can anyone advise as to why it gets paid off so much quicker in scenario 3?Assistant: The tool isnt smart enough to let you STOP extra payments. Youre paying 1041.67 extra every month until its paid off. In this case, thats 77 months for a total of 80,208.59.Human: Thank you. Youre totally right. See my comment above. Crap. So is there a better tool? Assuming the calculator was smart enough, would the savings come out identically? I guess what Im hoping for that its either the same or more beneficial to spread payments out over time mainly so I dont give up that 50k cushion. But now Im trying trying to get an apples to apples comparison that will show me how the interest savings will or wont add up over time.  <response>: They wouldnt come out the same. If you do a 50k lump sum payment, you never pay interest on that money anymore.By making the smaller payments, youll be paying an extra 120 in interest the first month, with that amount decreasing every month. In the 4 years it would take you to reach 50k total, youd pay an extra couple of thousand dollars in interest. Though that doesnt account for the fact you could invest the 50k right now. That could actually be better though will be riskier. 