IPMT vs PPMT: where each payment actually goes
Every fixed loan payment is the same size but a different mixture: IPMT returns the interest slice of payment N, PPMT the principal slice, and for any period they sum exactly to PMT. Early on you're mostly renting money; the mix flips past the halfway point.
The differences at a glance
| IPMT | PPMT | PMT | |
|---|---|---|---|
| Returns | Interest portion of payment N | Principal portion of payment N | The whole (constant) payment |
| Identity | IPMT + PPMT = PMT for every period — a built-in audit check | ||
| Over time | Shrinks each period | Grows each period | Constant |
| Cumulative versions | CUMIPMT over a period range | CUMPRINC | PMT x count |
| Compatibility | Universal | Universal | Universal (all verified by execution) |
Which should you use?
- IPMT — Tax-deductible interest for a year (or CUMIPMT for the range), interest-cost reporting, seeing what a month of the loan really costs.
- PPMT — Equity building, payoff progress, amortization schedule columns — one row per period with IPMT and PPMT side by side is the whole schedule.
Compatibility (from executed tests)
Executed on the same $300k/6%/30-year case in LibreOffice: IPMT(period 1) = exactly $1,500.00 (principal x monthly rate), PPMT = $298.65, and they sum to the verified PMT of $1,798.65 — identities intact across all versions we test. Sign conventions match Excel exactly (negative present value gives positive payments).
Example formulas
| Interest slice of month 1 | =IPMT(6%/12,1,360,-300000) |
| Principal slice of month 1 | =PPMT(6%/12,1,360,-300000) |
| A year of interest (months 13-24) | =CUMIPMT(6%/12,360,300000,13,24,0) |
Full per-version details on each function page: IPMT · PPMT · PMT.