What's new
New calculators and significant updates to existing tools.
0.181.0
In the BMI, VAT, mortgage and FIRE number calculators a required field left empty stays empty and waits for a value instead of showing a result from a default, and the mortgage sensitivity panel disappears until the fields are filled in. The history and privacy pages describe more precisely what is sent to the server when sync is on, that deleting an entry works only locally, and that some health calculators are never sent. Checkboxes in the contract calculators and comparisons no longer have nested labels, and CSV export and scientific notation no longer show a negative zero.
0.180.0
The Polish contract-for-work and mandate contract calculators have fields for the total amount in the contract and for a contract with your own employer, and contracts up to 200 zł with another payer are taxed at the 12% flat rate on the full amount, without costs, PIT-2 or the youth relief. The student over-limit notice appears only when tax is withheld, a negative base from other contracts shows a field error, and the contract comparison explains when the Labour and Solidarity Fund contributions are skipped below the minimum wage. Scientific notation uses a proper minus sign, and the PV kit inverter catalogue has a shorter note for ambiguous variants.
0.179.0
The Polish mandate contract calculator now withholds PIT for students under 26 on the part above the 85,528 zł youth relief limit and explains it in the result. When the contract is the only insurance title, the Labour and Solidarity Fund contributions apply only if this and other contracts reach the 2026 minimum wage in a full month, and the new fields are saved in the link and History. Page titles name the site only once, and screen readers no longer read the print report preview twice.
0.178.0
The Polish site Kalema has a new logo, icons and a refreshed home page. Search now finds calculators without diacritics, and the household budget is among the featured calculators. Calculator descriptions use the full width, and the PV kit configurator shows prices in pounds, euros or złoty with the VAT rates of each language version, including 0% for home solar in the UK and Germany.
0.177.0
The Polish version now runs as Kalema at kalema.pl, and old rivermath.com/pl addresses redirect to the new pages. Three calculators are new: a household budget with money flow, health ratios and the 50/30/20 rule, Polish inheritance and gift tax with tax groups, the close-family exemption and the SD-Z2 deadline, and flooring cost plus heating degree-days for gas.
0.176.0
The mortgage calculator has a clearer phone layout, correct interest saved with LTV insurance and overpayments, a better CSV name and a lighter page (translations for the current route only), and the savings goal counts whole months to the target. Lease has a richer manual simulation, and browsing historical offers is temporarily hidden. Less empty space in calculators and the footer, and the Geist font is served locally so the build no longer depends on Google Fonts.
0.175.0
A new e-commerce profit calculator works out profit per unit, net margin, markup and break-even price on Allegro, Amazon and your own shop, with category fees, payment gateways, shipping and income tax, and it is second on the home page next to the breathalyzer and alcohol units. The mortgage calculator has sliders, presets, a currency selector, insurance, overpayments, a balance chart and a paginated repayment schedule. The WHR and US Navy body fat calculators describe the waist measurement according to each model's protocol, separately for women and men.
0.174.0
The margin and markup calculator has three modes, VAT, marketplace fees and a price breakdown bar, and with a cost of 0 it shows the markup as undefined instead of 0%. The Polish zlecenie contract calculator keeps deductible costs to the grosz, so the PIT advance and net pay follow the rules, and the physics calculators show very large and small results as 1·10³⁰⁰ instead of 1E300. The PV inverter catalog lists the variant, source and date of each datasheet, and the mortgage report still prints the results after the preview is hidden.
0.173.0
History keeps empty fields and correctly restores the state of seven solvers, including Ohm's law. The quadratic equation solver computes roots in a way that avoids loss of digits, so a small root near −1 no longer comes out as 0. In the PV calculator, flat panels (0° tilt) give the same yield regardless of azimuth.
0.172.0
The FIRE number calculator now gives the time to the target even with a negative real return when contributions are high enough, and CAGR accepts an end value of 0 and shows −100%. The PV system size calculator checks roof fit using the whole number of panels, and the PV kit configurator has corrected current limits for GoodWe 8K/10K-ET inverters (12.5 A and 15.2 A per MPPT) and the correct number of inputs for Huawei SUN2000 MAP0 (2), so oversized strings now show a warning. In Ohm's law and the physics calculators very large and very small results use scientific notation, and a decimal comma also works in links.
0.171.0
The alcohol units calculator has drink categories with typical strengths and sizes, +/− buttons for the number of drinks, a list of several drinks with a breakdown for each and a total, calculation from product mass, equivalents shown as beers, wine and vodka, a handoff of the drinks to the breathalyzer calculator and copying of single results. In the Ohm's law calculator power is now an input: any two of the four quantities (voltage, power, current, resistance) give the other two, and presets for typical voltages and devices have icons and hints. In the AI subscriptions calculator, ChatGPT prices that OpenAI does not publish in a given currency are marked as estimated.
0.170.0
A new AI subscriptions calculator totals the monthly, yearly and daily cost of ChatGPT, Claude, Gemini, Grok, Perplexity, Copilot and custom tools in zloty, dollars or euros and points out overlapping plans. The salary, G11/G12 tariff comparison and buying power calculators show the data source, the period it applies to and the verification date, with a clear warning when data has no source or its period has ended. The solar payback calculator and the PV kit configurator have a live report preview with A4 printing, and the paint calculator works out cans, a waste allowance, windows and doors, and leftover paint.
0.169.0
A new household electricity calculator works out kilowatt-hours from a device list and the bill on the G11, G12 and G12w tariffs (at Energa also G12r and G11f) with the operators' 2026 distribution rates. A pilot adds A/B comparisons and scenarios, a richer calculation history, a solar planning path, worked explanations, goal-based navigation and printable reports for mortgages and PV. The calculation link after a handoff from the PV kit configurator now contains the numbers, subscription prices accept a decimal comma, and the unit converter has a button to swap units.
0.168.0
The PV kit configurator is first on the homepage and can pass system size, gross cost and whether a battery is included to the solar payback calculator. The numbers stay in this browser tab and are not put in the page address. Payback is shown in years and months, and the description uses the full page width.
0.167.0
The PV kit configurator builds the estimate from line items: each has a quantity and a net unit price, items can be added and removed, such as two batteries, and every category accepts a custom product with its own price. More powerful panels up to 575 W were added, mounting and labour quantities follow from the panels, and the result shows net, 8% or 23% VAT and gross amounts. Cables, connectors and protection are now optional accessories, and the design temperature field is gone from the form.
0.166.0
A new look for the homepage and calculator catalog in warm, earthy colours: search, topic browsing and a quick VAT calculator right at the start. Number fields and expandable explanations on phones are easier to use too.
0.165.0
New calculators: Polish property sale tax, home purchase costs, rainwater tank and septic tank emptying interval, plus multi-debt payoff strategy and the impact of investment fees on capital. The car cost of ownership calculator now covers powertrains (petrol, diesel, LPG, electric), depreciation, financing and a two-car comparison with payback time. Dates, numbers and keyboard accessibility work correctly in Polish, English and German.
0.164.0
Try BMI, VAT at 23% and a 2026 Polish salary estimate directly on the homepage. Open the full calculator with your chosen values. Catalog cards are lighter and calculator results are announced after you pause typing.
0.163.0
The weight-change calculator now has field hints for current weight, target weight and daily calorie balance.
0.162.0
The steps calculator now has field hints for step count, height and weight in the distance estimate.
0.161.0
The waist-to-hip ratio calculator now has field hints for tape-measure placement at waist and hip.
0.160.0
The body surface area calculator now has field hints for weight and height in the Mosteller formula.
0.159.0
The max heart rate calculator now has a field hint explaining that both age-based formulas share the same age input.
0.158.0
The protein target calculator now has field hints for body weight and grams per kilogram.
0.157.0
The Polish workdays calculator now has field hints for the date range and adding working days.
0.156.0
The child cost calculator now has field hints for monthly spend and the years counted.
0.155.0
The car running cost calculator now has field hints for mileage, fuel, insurance, service, purchase price and resale value.
0.154.0
The effective hourly pay calculator now has field hints for take-home pay, work hours, commute time and working weeks.
0.153.0
The rent vs buy calculator now has field hints for price, down payment, mortgage terms, housing costs, rent, horizon and growth assumptions.
0.152.0
The commute cost calculator now has field hints for distance, workdays, fuel use, prices, parking and a monthly ticket.
0.151.0
The hourly rate calculator now has field hints for conversion mode, pay amount, hours per week and weeks per year.
0.150.0
The savings goal calculator now has field hints for target, current balance, monthly deposit and annual rate.
0.149.0
The unit-price calculator now has field hints for both packs' price and quantity.
0.148.0
The margin and markup calculator now has field hints for cost and selling price.
0.147.0
The trip fuel calculator now has field hints for distance, consumption per 100 km and price per litre.
0.146.0
The bill split calculator now has field hints for the bill, number of people and optional tip percent.
0.145.0
The tip calculator now has field hints for the bill, tip percent and number of people.
0.144.0
The VAT calculator now has field hints for start direction, amount and tax rate.
0.143.0
The discount calculator now has field hints for the original price and percent off.
0.142.0
The dividend yield calculator now has field hints for share price, annual payout per share and number of shares.
0.141.0
The break-even calculator now has field hints for fixed costs, unit price and variable cost per unit.
0.140.0
The effective APR calculator now has field hints for the nominal rate and compounding frequency per year.
0.139.0
The rule of 72 calculator now has a field hint explaining the yearly rate and the 72 ÷ rate shortcut.
0.138.0
The real raise calculator now has field hints for salary, raise percent and inflation.
0.137.0
The annuity payment calculator now has field hints for principal, years and yearly rate.
0.136.0
The NPV calculator now has field hints for outlay, yearly cashflow, years and discount rate.
0.135.0
The CAGR calculator now has field hints for start value, end value and years.
0.134.0
The buying-power calculator now has field hints for amount, years, index mode and custom rate.
0.133.0
The compound interest calculator now has field hints for principal, rate, years, compounding and monthly deposits.
0.132.0
The real-return calculator now has field hints for nominal yield and inflation.
0.131.0
The future-price inflation calculator now has field hints for amount, annual rate and years.
0.130.0
The ROI calculator now has field hints for cost, current value and years held.
0.129.0
The rental yield calculator now has field hints for purchase price, rent, vacancy and running costs.
0.128.0
The BMI calculator now has field hints for weight and height.
0.127.0
The mortgage calculator now has field hints for home price, down payment, rate, term and instalment type.
0.126.0
The loan overpayment calculator now has field hints for principal, annual rate, term and extra monthly payment.
0.125.0
Subscriptions catalog: ChatGPT Go/Plus/Pro tiers and Google AI Plus/Pro/Ultra prices updated for PL, USD and EUR.
0.124.0
The simple payback calculator now has field hints for upfront cost and yearly savings or income.
0.123.0
Home and header search now answer simple payback phrases with years to earn back, e.g. “payback”, “prosty zwrot 24000” or “Einfache Amortisation”.
0.122.0
The debt payoff calculator now has field hints for balance, APR and monthly payment.
0.121.0
Home and header search now answer debt-payoff phrases with months to clear, e.g. “debt payoff”, “spłata długu 15000” or “Schulden tilgen”.
0.120.0
The FIRE number calculator now has field hints for yearly spend, withdrawal rate, current savings, yearly deposits and expected real return.
0.119.0
Home and header search now answer JDG Calendar phrases with annual take-home net, e.g. “jdg kalendarz 150”, “jdg calendar” or “JDG Kalender”.
0.118.0
New JDG Calendar calculator: net hourly rate × Polish workdays × 8 h, with ZUS, scale/linear/ryczałt and a monthly or quarterly year breakdown plus a workday chart.
0.117.0
Home and header search now answer FIRE number phrases with a nest-egg target, e.g. “fire number”, “liczba FIRE 60000” or “FIRE-Zahl 4%”.
0.116.0
The PV yield calculator now has field hints for array size, second-plane share and shading loss.
0.115.0
Home and header search now answer PV yield phrases with annual kWh, e.g. “pv yield”, “uzysk fotowoltaiki 10” or “photovoltaik ertrag warschau”.
0.114.0
The savings-rate calculator now has field hints for monthly take-home income and what you set aside each month.
0.113.0
Home and header search now answer savings-rate phrases with a percentage, e.g. “savings rate”, “wskaźnik oszczędności 6000 1200” or “sparquote 25%”.
0.112.0
The subscriptions calculator adds an AI category, more tiers, locale-specific prices and a tier price table with yearly totals and highlighted picks.
0.111.0
The emergency fund calculator now has field hints for monthly essentials, months of cover, cash already saved and monthly deposits.
0.110.0
Home and header search now answer emergency fund phrases with a cash target, e.g. “emergency fund”, “poduszka finansowa 4000” or “notgroschen”.
0.109.0
The PV sizing calculator now has field hints for annual use, cover share, module wattage and optional roof area.
0.108.0
Home and header search now answer PV sizing phrases with a suggested kWp, e.g. “fotowoltaika”, “pv size 10000” or “photovoltaik”.
0.107.0
The heat pump calculator now has field hints for heated area, insulation class, SCOP, gas price and boiler efficiency.
0.106.0
Home and header search now answer heat pump phrases with an annual running cost, e.g. “heat pump”, “pompa ciepła 150” or “Wärmepumpe wt 2021”.
0.105.0
Home and header search now answer subscription phrases with a monthly total, e.g. “subscriptions”, “subskrypcje netflix spotify” or “abos 100”.
0.104.0
Calculator links now use localized URL paths on Polish and German (e.g. /pl/subskrypcje, /de/abos); legacy English slugs redirect permanently.
0.103.0
The subscription calculator now has a catalog of popular services with tiers, brand marks, monthly or yearly billing and category totals.
0.102.0
Home and header search now answer heating-fuel phrases with the cheapest annual cost, e.g. “heating fuel” or “ogrzewanie 20000”.
0.101.0
The public changelog now lists only new tools and expansions of existing ones. The server-copy notice says only the site owner can read it, with a PIN.
0.100.0
Home and header search now answer insulation phrases with an annual heat-loss cost, e.g. “insulation 30”.
0.99.0
Home and header search now answer appliance-cost phrases with an annual total, e.g. “appliance 2000”.
0.98.0
The appliance energy calculator now has field hints for nameplate watts, daily hours and billing days.
0.97.0
Home and header search now answer cooling phrases with watts, e.g. “cooling 40”.
0.96.0
The heat-loss calculator now has field hints for U-value, temperature difference and heating-season hours.
0.95.0
Home and header search now answer water-bill phrases with a total, e.g. “water bill 9”.
0.94.0
The water and sewage bill calculator now has field hints for consumption, water tariff and sewage tariff.
0.93.0
Home and header search now answer hot-water phrases with an annual cost, e.g. “cwu 150”.
0.92.0
The heating fuel comparison calculator now has field hints for annual heat demand, boiler efficiency and heat-pump SCOP.
0.91.0
The cooling-load calculator now has field hints for floor area and watts per square metre, with typical 80–100 W/m² ranges.
0.90.0
The domestic hot water calculator now has field hints for inlet temperature, tap temperature and heater COP.
0.89.0
Home and header search now answer gas-bill phrases with a monthly total, e.g. “gas bill 80”. Gas queries no longer open the electricity bill calculator by mistake.
0.88.0
The gas bill calculator now shows the standing charge separately from energy cost and adds field hints for the calorific factor and monthly fixed fee.
0.87.0
English and German catalogues now hide Poland-specific tools such as G11 tariffs and employment-contract pay. Those calculators stay under Poland’s flag; search still finds them.
0.86.0
The G11 vs G12 calculator now has info icons with field hints for the distributor, peak share and seller energy prices.
0.85.0
The power bill calculator now groups seller energy, DSO distribution and net-billing separately, and adds info icons with hover hints on less obvious fields.
0.84.0
The G11 vs G12 calculator now includes an infographic of weekday peak hours and how your annual use splits between peak and off-peak on G12.
0.83.0
Power bill queries now show the estimated annual bill inline in home and header search, with the tariff used in the estimate.
0.82.0
G11 vs G12 queries now show estimated annual savings inline in home and header search, with a note on which tariff wins.
0.81.0
Contract comparison queries now show the best take-home pay inline in home and header search, with a note on which form wins.
0.80.0
Home search now understands contract comparison phrases and opens the UoP vs zlecenie vs JDG calculator, optionally prefilling monthly gross from your query.
0.79.0
Home search now understands electricity bill phrases and opens the power bill calculator, optionally prefilling yearly use, G11/G12 tariff or peak share.
0.78.0
Home search now understands G11 vs G12 phrases and opens the tariff comparison calculator, optionally prefilling yearly use or peak share from your query.
0.77.0
New G11 vs G12 tariff comparison calculator with distributor presets (PGE, Tauron, Enea, Energa, STOEN), 2025 net distribution rates and a side-by-side yearly bill. Pick your DSO, enter use and seller prices to see which tariff saves more.
0.76.0
Date and time fields now select their value when you focus them, like the number inputs. Tap a drink time in the breathalyzer and you can type over it right away.
0.75.0
The Browse chevron turns when the menu is open, the same way FAQ questions do. Tabbing to Browse shows the header focus ring, so you can tell the control is selected.
0.74.0
Remove on a saved result now names the calculator. You can tell BMI from VAT before you delete a row.
0.73.0
The RiverMath mark in the header looks selected on the home catalog. The same mark in the footer is a home link, so you can get back without hunting for Calculators.
0.72.0
Footer links for history, privacy, cookies, changelog, groups and topics look selected on the page you are on. Screen readers hear the current page in the footer the same way as in the header.
0.71.0
Header search shows how many calculators match what you typed. The list is a combobox, so arrow keys and screen readers stay on the same row.
0.70.0
Group chips on the home catalog highlight the section you are looking at. The sticky bar keeps the current group in view on a narrow screen.
0.69.0
The appearance control in the header shows light, dark or match system next to the icon. You no longer have to hover to see which theme is on.
0.68.0
The version in the footer is a link to that release on the changelog. Each release heading is a permalink, and the sticky header does not cover it.
0.67.0
Browse in the header looks selected on a group or calculator page. Opening it highlights the current group and tool as the current page.
0.66.0
History and About look selected in the header and phone menu when you are on those pages. Group and topic links in the phone menu do the same. Screen readers mark the language chip as the current page.
0.65.0
Topic chips now sit under a heading in the page language. The active topic is marked as the current page.
0.64.0
Number fields no longer show browser stepper arrows. Those controls crowded the unit suffix and fought tap-to-replace.
0.63.0
Header search shows a / key. Pressing it focuses the search you can see, not the hidden copy for the other layout.
0.62.0
Search no longer goes quiet when nothing matches. The dropdown stays open and says that no calculators fit what you typed.