Home energy upgrade loan calculator
Work out the monthly payment and total interest on a loan for a home energy upgrade, and compare it with expected savings.
A $20,000 loan at 8% APR over 10 years costs $242.66 a month, or $9,119 in total interest (example values; enter your offer).
- Monthly payment
- $242.66
- Total interest
- $9,119
- Total paid
- $29,119
| Year | Interest | Principal | Balance |
|---|---|---|---|
| 1 | $1,551 | $1,361 | $18,639 |
| 2 | $1,438 | $1,474 | $17,165 |
| 3 | $1,316 | $1,596 | $15,569 |
| 4 | $1,183 | $1,729 | $13,840 |
| 5 | $1,040 | $1,872 | $11,967 |
| 6 | $884.11 | $2,028 | $9,940 |
| 7 | $715.81 | $2,196 | $7,744 |
| 8 | $533.54 | $2,378 | $5,365 |
| 9 | $336.14 | $2,576 | $2,790 |
| 10 | $122.35 | $2,790 | $0.00 |
Formula: payment = P × r ÷ (1 − (1 + r)^−n), where P is the amount, r the monthly rate (APR ÷ 12) and n the number of monthly payments.
Inputs used: amount: $20,000; APR: 8%; term: 10 years.
These are estimates, not financial advice.
Worked examples
| Scenario (example values) | Monthly payment | Total interest | Total paid |
|---|---|---|---|
| $10,000 heat pump, 5 years at 7% | $198.01 | $1,881 | $11,881 |
| $20,000 solar, 10 years at 8% | $242.66 | $9,119 | $29,119 |
| $30,000 solar + battery, 15 years at 9% | $304.28 | $24,770 | $54,770 |
How we calculate
payment = P × r ÷ (1 − (1 + r)^−n) with r = APR ÷ 12 and n = years × 12; at 0% APR, payment = P ÷ n. Interest is calculated monthly on the remaining balance.
Frequently asked questions
How is the monthly payment calculated?
With the standard amortization formula: payment = P × r ÷ (1 − (1 + r)^−n), where P is the loan amount, r the monthly interest rate (APR ÷ 12) and n the number of payments.
Should the energy savings cover the payment?
If the monthly savings exceed the payment, the upgrade is cash-flow positive from the first month. Enter the annual savings from one of our calculators to compare. Remember savings estimates are uncertain while the loan payment is fixed.
Does this include fees?
Only if they are reflected in the APR you enter. Origination fees, dealer fees and prepayment terms can change the true cost; compare offers by APR and total paid.
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