Mortgage Tipping Point Calculator: Principal vs Interest

Find your rate on the left and your term across the top. Each cell is the number of the first payment in which principal exceeds interest, and a 1 means principal leads from the start.

Computed by this site for fixed-rate loans with level monthly payments and no extra principal, and checked against a month-by-month schedule. 7.24% and 6.60% are Freddie Mac's PMMS 30-year and 15-year averages for the week of October 29, 2026; the other rates are round reference points.

Read across any row, past the 1s, and something odd appears: from one term to the next, the tipping payment rises by exactly 60, the number of payments in the five extra years. Payment 246 on a 30-year loan, 186 on a 25-year, 126 on a 20-year. That is no coincidence. At a given rate, the tipping point always falls the same number of payments before the end of the loan. At 7.24% there are 114 payments left after it, whatever the term.

The 1s in the top left are the edge case. When a loan is short enough, or the rate low enough, that interest never takes half of a payment, there is no flip to wait for. The condition is that (1 + r)^N is 2 or less, which means rates up to about 6.95% for 10 years, 4.63% for 15, 3.47% for 20, 2.78% for 25 and 2.31% for 30.

Call the monthly rate r, the number of payments N, and the level payment M. The derivation needs no more than the way a schedule works.

1. Principal grows by a fixed factor. Each month's interest is r times the balance. Paying P of principal this month removes rP of interest from next month, and that rP moves over to principal. So next month's principal is P(1 + r).
2. The last payment fixes the scale. Before the final payment the balance is M ÷ (1 + r), because that amount plus one month of interest on it equals M. So the principal in the last payment is M ÷ (1 + r).
3. Work back from the end. Stepping back one payment divides principal by (1 + r), so the principal in payment k is M(1 + r)^{k − 1 − N}.
4. State the condition. Principal exceeds interest when principal is more than half of M, so (1 + r)^{k − 1 − N} must be more than 1/2.
5. Take logs. That gives k > N + 1 − ln 2 ÷ ln(1 + r). The tipping payment is the next whole number above that value, or payment 1 if the value is below 1.

Now try it at 7.24%: r = 0.0724 ÷ 12, and ln 2 ÷ ln(1 + r) = 115.23. So 360 + 1 − 115.23 = 245.77, and the next whole payment is 246. The schedule for an illustrative $400,000 loan with a $2,725.99 monthly payment agrees. Payment 245 is $1,369.27 of interest and $1,356.72 of principal. Payment 246 is $1,361.09 of interest and $1,364.90 of principal.

The middle term has a plain meaning: 115.23 is the number of months money takes to double at this rate, and principal in a payment doubles over the same stretch. So the tipping point sits one doubling time before the end of the loan, since by the last payment principal is close to the whole of M, and half of that is one doubling back. This is why a table cell depends on the rate and term alone.

There is a second test you can run with a statement in hand. Interest is rB on a balance B, so principal leads once B is below M ÷ (2r). On the example, that tipping balance is $225,910.99; the balance before payment 246 is $225,594.82, and the balance before payment 245 was still above the line. A mortgage tipping point calculator uses this in today's-balance mode, where the original term may be unknown. The closed form was tested against a full schedule on 3,200 rate and term pairs, with terms of 5 to 40 years and rates from 0% to just under 20%, and they matched every time.

These are two different milestones, and mixing them up is easy. The tipping point is about the split inside one payment. Paying off half the balance is about the debt as a whole, and it is the subject of how long it takes to pay off half of a 30-year mortgage. On a mortgage with interest in it, the tipping point always comes first.

30-year fixed loans with level monthly payments and no extra principal; share computed on an illustrative $400,000 and the same at any loan size. 7.24% and 6.60% are PMMS averages for the week of October 29, 2026; the 6.60% average is the 15-year figure, used here as a reference rate. Half-balance payment is the first payment that takes the balance to half the original loan or lower.

The gap closes as rates rise. At 3% the two are 136 payments apart, more than eleven years. At 10% they nearly touch. Either way, the tipping point is the earlier and less demanding test: at 7.24% more than half of the loan is still owed the day principal takes the lead.

A fixed payment cannot change the rate or the term, but it can change the split. Any extra principal lowers the balance, so interest falls sooner, and the extra itself counts on the principal side of the comparison. That second effect is why even small amounts move the date so far.

Illustrative $400,000, 30-year fixed at 7.24% (PMMS, week of October 29, 2026), extra paid from the first payment and counted as principal. Computed by this site.

Crossing the tipping point sooner is a by-product and never a goal in itself. The real gain from extra payments is the interest saved and the earlier payoff, which the schedule with extra payments shows line by line. Nothing happens to your cost when the split flips: your payment, rate and balance carry on as before. It is a useful marker for seeing how far along you are, and the mortgage tipping point calculator is the quickest way to find yours. To see the numbers on either side of it, the full amortization schedule prints every payment.