The number nobody
wants to give you
The number nobody wants to give you is the honest one. Three free tools for decisions where that matters more than encouragement. No account, no email, and nothing you type is sold to anybody. Every figure names its source.
七転び八起き
The tools
Each one exists because the honest version of the answer was hard to find anywhere else. Two of them do arithmetic on money: rooftop solar payback, and the full cost of a mortgage, loan or plan. The third checks whether AI search engines can read and cite a website at all. All three run in the browser and store nothing.
Solar Straight
What rooftop solar actually costs and when it pays for itself, using NREL production data and your own utility's filed rate. The federal credit is set to zero, exports are valued at nothing, and if the system never pays back inside 25 years it says never.
Open 02FinCalc
Eleven calculators for mortgages, loans, debt, savings and retirement that show the complete number rather than a flattering part of it. A mortgage payment here includes tax, insurance, PMI and HOA, with PMI ending automatically at 78% loan-to-value, as the law requires.
Open 03AnswerRank
Whether ChatGPT, Claude and Perplexity can read, quote and cite your site. GEO, AEO, AIO, LLMO, AISO, GAIO, AISEO, AAO, ChatGPT SEO: nine names for one job, measured across 30 signals fetched as the crawlers themselves, with the weights published and the fixes written for your page.
Open| Tool | The question it answers | Primary sources |
|---|---|---|
| Solar Straight | Will rooftop solar pay for itself here, and in what year? | NREL PVWatts v8, EIA retail prices, NREL Annual Technology Baseline |
| FinCalc | What will this loan, mortgage or plan actually cost me? | Your own figures; statutory thresholds such as PMI ending at 78% LTV |
| AnswerRank | Can ChatGPT, Claude and Perplexity read and cite my site? | Your page, fetched as each crawler; the KDD 2024 GEO study for four checks |
Through rigorous evaluation, we demonstrate that GEO can boost visibility by up to 40% in generative engine responses.
Aggarwal et al., GEO: Generative Engine Optimization, KDD 2024, arXiv:2311.09735
Why are free calculators so optimistic?
Nearly every free tool on the internet pays for itself somehow. A great many pay for themselves by collecting you. The calculator is the bait, your contact details are the product, and they are sold to whoever wants to sell you something. That model has a consequence people rarely notice: the tool has to give an encouraging answer, because a discouraging one produces fewer leads.
So you get a whole category of software that leans one way:
- Solar estimators still subtracting a 30% federal credit that ended for purchases after 31 December 2025. On a $28,000 system that is $8,400 of savings that no longer exist.
- Mortgage calculators quoting principal and interest only. Add property tax, insurance and PMI and the real payment is often 25% to 33% higher.
- Solar payback tools assuming electricity prices rise 3.5% a year. The EIA measured 2.9% from 2013 to 2023, and under 1% after inflation. Over 25 years that gap can be the difference between paying back and never paying back.
Retail electricity prices closely tracked inflation over the last 10 years.
U.S. Energy Information Administration, Today in Energy
None of it is quite a lie. It is an answer to a more comfortable question than the one you asked. These tools collect nothing, so they have no reason to flatter you. Sometimes that means saying solar will never pay for itself where you live. That is the point.
The mechanism is worth understanding in detail, because once you can see it you can check any tool in about a minute: why free calculators flatter you.
What rules does every tool follow?
Four, and they are checked before anything ships. They are also the reason results here are sometimes worse than results elsewhere. A calculator that follows them cannot round in your favour, cannot fill a gap with an average, and cannot hide the step you would have argued with. That is the whole design.
Nothing is invented
Where a figure comes from a government dataset or a published source, that source is named on the page with the date it was checked. Where something is genuinely an assumption, it is labelled as one and you can change it.
Refusing beats guessing
If a tool cannot get the data it needs, it says so rather than substituting an average and presenting the result with the same confidence. A plausible wrong answer is worse than no answer when real money is involved. An honest blank is a result too.
The workings are published
Every calculation has a methodology page or a printed formula, with the inputs listed in the order they are used. You should never have to take a number on trust when you could check it instead. If a step looks wrong to you, it is there to be argued with.
The limits are stated
Each tool says plainly what it cannot see: the tree shading your roof, your tax position, whether your job is secure. These handle the arithmetic so your attention goes to the parts that are judgement. Nothing here replaces a person who knows your situation.
Questions people actually ask
Are these tools really free?
Yes. There is no account, no trial, no paywall and no upgrade. The tools are paid for by ordinary display advertising, which does not require knowing anything about you.
Do I have to give an email address?
No. No tool on this site asks for an email address, a phone number or a name, and none of them will. The figures you type are used to produce your result and are not stored or sold.
Why are your solar payback figures worse than other calculators?
Because three things most calculators omit are included. The federal tax credit is zero, since IRC Section 25D was terminated for expenditures after 31 December 2025. Electricity prices are assumed to rise 2.9% a year, the rate the EIA actually recorded, rather than the conventional 3.5%. And upkeep is charged at $30 per kW per year, where most tools charge nothing.
Where do the figures come from?
Production data comes from NREL PVWatts v8. Electricity prices and their growth rate come from the US Energy Information Administration. Maintenance costs come from NREL's Annual Technology Baseline. Every source is named on the tool's methodology page with the date it was last checked.
Who built this?
One person: Sastihari S, a software engineer in India. Not a financial adviser, a solar installer or an SEO consultant, and with no commercial relationship to any company in those industries. Nothing here earns a commission on your decision.
Can a tool here tell me not to do something?
Yes, and that is the point. The solar calculator reports never when an installation will not pay for itself inside twenty-five years, instead of extending the horizon until the answer turns positive.
What each tool will not do
The limits are the same across all three, and they are deliberate.
- Ask who you are. No account, no email field, no phone number, on any tool.
- Store what you type. Your figures produce your result and are then gone.
- Invent a number. Where no data exists, the tool says so instead of filling the gap with an average.
- Hide an assumption. Every growth rate, tax treatment and cost is published and can be changed.
- Pretend to see what it cannot. Shading, your job security and your tax position are named as blind spots rather than guessed at.
Who built this, and who pays for it?
I am a software engineer, not a financial adviser, a solar installer or an SEO consultant, and I have no commercial relationship with any company in those industries. Each of these began because I wanted an honest answer to something and could not find one that was not attached to a sales funnel.
If a number here is wrong, I would rather be told than be right. There is more on the about page, and you can get in touch directly.
Written and maintained by Sastihari S, software engineer and builder.
What do the notes cover?
How each tool works and why its answers differ from the usual ones. Five articles, each one long enough to check the arithmetic.
- Why free calculators flatter you 8 min
A free tool has to be paid for somehow, and the usual arrangement quietly requires the answer to be encouraging. The mechanism, and how to spot it. - How solar payback is actually calculated 11 min
The arithmetic is simple. Every disagreement between two quotes comes from four assumptions, and one of them changed in 2025. - What your mortgage payment leaves out 9 min
The figure on the listing is principal and interest. The figure that leaves your account is usually a third larger, and the gap is predictable. - What an AI assistant sees when it reads your site 10 min
Not what you see. Most assistants read the HTML your server sends and never run your JavaScript, so a site can be perfectly visible to a person and blank to a machine. - Where these numbers come from 7 min
Every dataset behind the three tools, who publishes it, when it was last checked, and what happens when a source cannot be reached.
All of them, with dates, are on the notes page.