Principal Only Payment Calculator
Every mortgage payment is two payments wearing one disguise: the interest portion, which vanishes into the lender’s pocket, and the principal portion, which builds your equity. A principal-only payment strips away the disguise — an extra payment applied 100% to the loan balance. Because interest is charged on the balance, every principal-only dollar shrinks all future interest charges too.
The Principal Only Payment Calculator on this page quantifies exactly what your extra payments buy. Enter balance, rate, regular payment, and extra principal-only amount to see new payoff time, time saved, interest before and after, and return on each extra dollar.
What Is a Principal-Only Payment?
A principal-only payment (principal curtailment) is an additional payment directed entirely at reducing the loan’s principal balance. Unlike your regular payment — split between interest and principal — a principal-only payment bypasses interest completely. If you send $200 marked “principal only,” your balance drops by exactly $200.
This differs from paying early: unlabeled early payments may be treated as regular payments or held as credit. Always confirm with your servicer that extra funds are applied to principal. It also differs from recasting, which re-amortizes a smaller balance into lower payments.
Why Principal-Only Payments Matter
The power comes from the interest-on-balance mechanism. Reduce the balance by $200 today, and next month’s interest falls by $200 × monthly rate — and every subsequent month’s too. One payment echoes through the entire schedule.
The return is guaranteed and risk-free: paying down a 6.5% mortgage earns 6.5% on every extra dollar. There is also a flexibility advantage over refinancing to a shorter term — prepayments are voluntary and can be paused.
How to Use the Calculator
Step 1: Enter current loan balance (e.g., 300000).
Step 2: Enter annual interest rate (e.g., 6.5).
Step 3: Enter regular monthly P&I payment (e.g., 1896).
Step 4: Enter extra principal-only payment/month (e.g., 200).
Step 5: Click Calculate to compare both schedules.
Worked Example: $300,000 at 6.5%, $200/Month Extra
Baseline: 360 months, total interest ≈ $382,560. With $200 extra: payoff in ~283 months (23 yrs 7 mos). Time saved: 77 months (6 yrs 5 mos). Interest saved: ~$103,500. Total extra paid: $56,600. Return: ~183% — every extra dollar eliminated $1.83 of interest.
Making Sure Extra Payments Hit Principal
Label every extra payment explicitly — write “principal only” or select the option online. Verify on your next statement that the balance dropped by the full extra amount. Watch for prepayment penalties (rare) and confirm any minimum extra amount or special processing address.
Principal-Only vs. Other Uses of Cash
Allocate deliberately: high-interest debt first (credit cards at 20%+), emergency fund second (3–6 months), retirement matching third (instant 50–100% return). Beyond that, prepaying earns a guaranteed rate equal to your mortgage interest vs. investing’s uncertain returns. Extra mortgage payments are illiquid — money is trapped as equity.
Tips
- Always designate “principal only.”
- Verify on statements.
- Start small if needed. Even $50–$100/month shortens a 30-year loan.
- Automate the extra.
- Time lump sums early. Early-year bonuses save the most.
- Check for prepayment penalties.
- Prioritize toxic debt first.
Frequently Asked Questions
1. What is a principal-only mortgage payment? An extra payment applied entirely to the loan balance.
2. How do I ensure extra goes to principal? Label it “principal only,” confirm with servicer, verify on statements.
3. How much can extras save? On $300k/6.5%/30yr: $200/mo saves ~$103,500 and 6.4 years.
4. Do principal-only payments lower my payment? No — they shorten the loan. Recasting lowers payments.
5. Should I prepay or invest? After debt, emergencies, and matches: prepaying is guaranteed; investing is uncertain.
CONCLUSION
Principal-only payments are a financial superpower: every extra dollar hits the balance, every reduced balance shrinks future interest, and the return — your mortgage rate, guaranteed — beats nearly every safe alternative. Start modestly; the earliest dollars earn the highest returns.