mortgages additional payments or lump sums?

There are online calculators that you can play with.

If you choose to pay your mortgage early, pay it when the funds are available.

See wickowick's comment re: interest rates. If after the tax break on interest payments your effective rate is below inflation, you are better off not prepaying at all.

For example, if your rate is 4.4% and you're in the 25% tax bracket, your post-tax rate is really 3.3%. If you think inflation over the next 30 years will be greater than this, don't prepay.

If you prepay anyway (whether you should or not) then again it depends on the rate. If you shouldn't be prepaying by the above calculation, delay the payment for as long as possible by doing a lump sum at the end of the year. If you should be prepaying, do the lump sum at the start of the year or at least as much of it as you can as early as you can.

We bought our first home in 2004. Paid double mortgage payments every month and then extra principal in dec each year. Paid it off in 7 years with a 20k lump sum at end

I just started doing this in February. Been paying my regular note but applying everything I make at my side job towards principle. I figured if I payed an extra $750 per month I would pay off 11 years early and save 61 k in interest.