Is It Worth It? Running the Numbers
A refinance that saves $435 a month can cost $53,064 more in interest. Both are true - the window you choose decides which one you see.
The tools in this guide
All free, no signup. Each one has a printable sheet too.
- ROI and Payback Period CalculatorPayback ignores everything after it pays back. ROI ignores when the money arrives. You need both, and they disagree.
- Refinance Break-Even CalculatorHow many months to recoup the closing costs - and whether a lower payment is actually costing you more over the life of the loan.
- Lease vs Buy Car CalculatorCompared over the same period, the two are usually much closer than they look - and the whole answer hinges on a resale value nobody knows.
Three decisions, one shape: pay something now, get something back over time. Whether it is "worth it" is not a fact about the deal — it is a fact about the window you measure over, and that is what these tools make visible.
The clearest case: a refinance
The Refinance Break-Even Calculator produces two figures that both look decisive and point opposite ways.
A $300,000 balance, 6.5% → 5.5%, $4,500 of closing costs:
| Payment now | $2,138.82 |
| Payment after | $1,703.37 |
| Monthly saving | $435.45 |
| Break-even on the closing costs | 10.3 months |
| Net gain over 5 years | $21,627 |
Refinance, obviously.
Except:
| Change in total interest | +$53,064 |
| Extra months of payments taken on | 96 |
Both numbers are correct. The saving is real, and so is the extra $53,064 — because resetting a loan with 264 months left back to 360 months adds eight years of payments. You bought a lower payment with a longer term.
⚠️ Neither figure is "the answer." If you are moving in five years, the $21,627 is what happens to you and the total-interest figure is hypothetical. If you will hold the loan to the end, the reverse. The window decides, and the tool shows both because the industry usually shows only the first.
When the payback is the whole story
The ROI and Payback Period Calculator handles the case where the thing genuinely pays for itself.
A $10,000 investment returning $1,200 a month against $200 of running costs:
| Net return a month | $1,000 |
| Pays for itself in | 10 months |
| Return over 24 months | 140% |
| — annualised, roughly | 70% |
| Months actually in profit | 14 of 24 |
That last row is the one worth pausing on. Over a two-year horizon, ten of those months are spent getting back to zero. A 140% return sounds like the whole period was productive; it wasn't.
⚠️ Running costs matter more than they look. Here they eat 17% of the return — and unlike the up-front investment they never stop. A payback calculation that ignores them flatters every option that has them.
The tool also reports what you'd need to earn monthly to pay back inside your horizon: $616.67. That is the honest hurdle, and it's a much better question than "what's the ROI."
When the answer is "they're the same"
The Lease vs Buy Car Calculator compares over the only span where both options exist — the lease term.
A $35,000 car, $5,000 down at 6.5% over 60 months, against a $450/month lease:
| Lease, total over 36 months | $19,600.00 |
| Buy, net cost over the same 36 | $19,308.41 |
| Difference | $291.59 |
Two hundred and ninety-one dollars, over three years. On typical numbers these are far closer than the monthly payments suggest — and the loan payment is $136.98 a month higher, which is the number that sells leases and the one that means least.
The reason they're close is the part the monthly comparison hides: at month 36 you hold $6,823 of equity against $13,177 still owed. Leasing hands the car back and that equity is the entire difference.
⚠️ And one guess moves everything. Every other input is contractual. Resale value is a forecast about a used-car market three years out — move it $5,000 either way and the answer flips. Run it pessimistically as well as realistically; if buying only wins on the optimistic number, it doesn't really win.
The pattern across all three
| Tool | The number that sells it | The number that qualifies it |
|---|---|---|
| Refinance | $435/month saved | +$53,064 total interest |
| ROI | 140% return | 10 months just getting to zero |
| Lease vs buy | $137/month cheaper | $6,823 of equity given up |
In every case the persuasive figure is the short-window, cash-flow one, and the qualifying figure is the long-window, total-cost one.
Neither is dishonest. But the short-window number is the one that gets quoted to you, so the long-window number is the one you have to go and get.
How to actually use these
- Decide your window first, before you run anything — how long will you really keep this?
- Run it at that window, then run it at half and double.
- If the answer changes sign, you have not found an answer. You have found that the decision rests on a forecast, and the honest move is to ask how confident you are in it.
General information, not financial advice. For a commitment of this size, talk to a qualified adviser.
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