Methodology and accuracy policy
Every result on Hisaab can be checked by hand. This page explains the formulas, the sources and how we keep them correct.
How we keep results accurate
- Official sources only. Rates come from the Finance Act and FBR, NEPRA notifications, the State Bank of Pakistan and published scholarly methods. Each calculator page lists its sources.
- One data file per rate set. Tax slabs and tariffs are stored once and used by every page, so an update cannot leave one page behind.
- Automated tests. Every calculator is tested against worked examples, such as published tax figures and classical inheritance cases, before any change goes live.
- Fast updates. On budget day and after each NEPRA notification we update the rates, label proposed figures as proposed until they are final, and change the "Updated" date on the page.
- Error reports. If you spot a mistake, tell us. Confirmed errors are fixed as a priority.
How each calculator works
| Calculator | Method | Source |
|---|---|---|
| Salary tax calculator | Annual salary is matched to the 2026-27 slab for salaried individuals. Tax = the slab's fixed amount + its rate × the income above the slab's start. The previous year (with any surcharge) is calculated the same way for comparison. | Finance Act, First Schedule, Part I, Division I (FBR) |
| LESCO bill calculator | Protected consumers are billed slab by slab; unprotected consumers pay the rate of the slab reached on every unit. Fixed charges = rate per kW × sanctioned load. Fuel adjustment = rate × units. GST is added on the total. One uniform tariff applies to every DISCO and K-Electric. Tariff effective 2026-02-12. | NEPRA tariff notification (SRO 279(I)/2026); Sales Tax Act 1990 |
| Solar size & payback | Size = monthly units ÷ 120 units per kW (about 5 peak sun-hours at 80% efficiency), rounded up to 0.5 kW. Saving = self-used units × your unit price + exported units × buyback rate. Payback = cost ÷ yearly saving. | NEPRA Prosumer (net billing) Regulations 2026; installer price quotes |
| Zakat calculator | Zakatable assets minus debts due now are compared with the nisab (52.5 tola silver or 7.5 tola gold at the price you enter). If at or above nisab, zakat = 2.5%. | Classical Hanafi fiqh; Zakat and Ushr Ordinance 1980 |
| Inheritance calculator | Debts are paid first, then any will up to one-third. Fixed Quranic shares are assigned, the residue goes to residuary heirs (sons with daughters at 2:1, then father, then siblings), with 'awl, radd (excluding the spouse) and 'Umariyyatain applied as in the Hanafi school. Exact fractions are used throughout. | Quran 4:11, 4:12, 4:176; Al-Sirajiyyah |
| Marla converter | All units convert through square feet: Marla = 225, 250 or 272.25 sq ft (your choice), Kanal = 20 Marla, square yard = 9 sq ft, square metre = 10.7639 sq ft, acre = 43,560 sq ft. | Punjab Land Revenue measures; housing society standards |
| Construction cost calculator | Cost = covered area × (grey structure rate + finishing rate), plus a contingency percentage. Default rates are published 2026 Lahore builder rates and can be edited. | Builder rate surveys, Lahore 2026 |
| Car loan calculator | Reducing-balance installment: P × r × (1+r)^n ÷ ((1+r)^n − 1), with r = annual rate ÷ 12 and n = months. Insurance and fees are not included. | SBP Prudential Regulations for Consumer Financing |
| Committee (BC) calculator | Pot = members × monthly amount. Each member receives the pot once, in turn order, one month apart. | Standard rotating savings (ROSCA) model |
| Govt job age calculator | Age is counted in completed years, months and days on the closing date. A limit of "N years" is treated as not having reached the next birthday after age N, after adding any relaxation you enter. | FPSC and provincial commission advertisement rules |
Limits
Calculators give estimates for guidance. Your actual tax, bill or entitlement can differ because of exemptions, adjustments, arrears or facts the calculator does not ask about. Zakat and inheritance follow mainstream Hanafi methods; rulings can differ between schools of thought, so consult a qualified scholar for complex cases. For official decisions, rely on the relevant authority or a qualified professional.
This page covers all 10 calculators. Last reviewed 12 October 2026.