Calculators
Four everyday calculations for small-business finance. Every result shows its working: the formula, the numbers that went in and each rounded step, so you can check it or paste it into a file note. Everything runs on your device. Nothing you type is sent anywhere, and it works offline.
Tax: add or remove
GST, VAT or sales tax at any rate.
| Step | Working | Result |
|---|---|---|
| Net amount (before tax) | entered | 1,000.00 |
| Tax | 1,000.00 × 10% | 100.00 |
| Gross amount (tax included) | 1,000.00 + 100.00 | 1,100.00 |
Margin and markup
Margin is profit as a share of the selling price; markup is profit as a share of cost.
| Step | Working | Result |
|---|---|---|
| Cost | entered | 80.00 |
| Selling price (before tax) | entered | 100.00 |
| Gross profit | 100.00 − 80.00 | 20.00 |
| Margin | 20.00 ÷ 100.00 × 100 | 20.00% |
| Markup | 20.00 ÷ 80.00 × 100 | 25.00% |
Loan or lease repayment
Equal monthly payments (annuity method), interest charged monthly on the balance.
| Step | Working | Result |
|---|---|---|
| Amount borrowed | entered | 50,000.00 |
| Monthly rate r | 9.5% ÷ 12 | 0.791667% |
| Monthly payment | P × r × (1+r)^36 ÷ ((1+r)^36 − 1) | 1,601.65 |
| Last payment (absorbs rounding) | 12.58 + 1,588.98 | 1,601.56 |
| Total paid | sum of 36 payments | 57,659.31 |
| Total interest | 57,659.31 − 50,000.00 | 7,659.31 |
Show the repayment schedule (36 months)
| Month | Payment | Interest | Principal | Balance |
|---|---|---|---|---|
| 1 | 1,601.65 | 395.83 | 1,205.82 | 48,794.18 |
| 2 | 1,601.65 | 386.29 | 1,215.36 | 47,578.82 |
| 3 | 1,601.65 | 376.67 | 1,224.98 | 46,353.84 |
| 4 | 1,601.65 | 366.97 | 1,234.68 | 45,119.16 |
| 5 | 1,601.65 | 357.19 | 1,244.46 | 43,874.70 |
| 6 | 1,601.65 | 347.34 | 1,254.31 | 42,620.39 |
| 7 | 1,601.65 | 337.41 | 1,264.24 | 41,356.15 |
| 8 | 1,601.65 | 327.40 | 1,274.25 | 40,081.90 |
| 9 | 1,601.65 | 317.32 | 1,284.33 | 38,797.57 |
| 10 | 1,601.65 | 307.15 | 1,294.50 | 37,503.07 |
| 11 | 1,601.65 | 296.90 | 1,304.75 | 36,198.32 |
| 12 | 1,601.65 | 286.57 | 1,315.08 | 34,883.24 |
| 13 | 1,601.65 | 276.16 | 1,325.49 | 33,557.75 |
| 14 | 1,601.65 | 265.67 | 1,335.98 | 32,221.77 |
| 15 | 1,601.65 | 255.09 | 1,346.56 | 30,875.21 |
| 16 | 1,601.65 | 244.43 | 1,357.22 | 29,517.99 |
| 17 | 1,601.65 | 233.68 | 1,367.97 | 28,150.02 |
| 18 | 1,601.65 | 222.85 | 1,378.80 | 26,771.22 |
| 19 | 1,601.65 | 211.94 | 1,389.71 | 25,381.51 |
| 20 | 1,601.65 | 200.94 | 1,400.71 | 23,980.80 |
| 21 | 1,601.65 | 189.85 | 1,411.80 | 22,569.00 |
| 22 | 1,601.65 | 178.67 | 1,422.98 | 21,146.02 |
| 23 | 1,601.65 | 167.41 | 1,434.24 | 19,711.78 |
| 24 | 1,601.65 | 156.05 | 1,445.60 | 18,266.18 |
| 25 | 1,601.65 | 144.61 | 1,457.04 | 16,809.14 |
| 26 | 1,601.65 | 133.07 | 1,468.58 | 15,340.56 |
| 27 | 1,601.65 | 121.45 | 1,480.20 | 13,860.36 |
| 28 | 1,601.65 | 109.73 | 1,491.92 | 12,368.44 |
| 29 | 1,601.65 | 97.92 | 1,503.73 | 10,864.71 |
| 30 | 1,601.65 | 86.01 | 1,515.64 | 9,349.07 |
| 31 | 1,601.65 | 74.01 | 1,527.64 | 7,821.43 |
| 32 | 1,601.65 | 61.92 | 1,539.73 | 6,281.70 |
| 33 | 1,601.65 | 49.73 | 1,551.92 | 4,729.78 |
| 34 | 1,601.65 | 37.44 | 1,564.21 | 3,165.57 |
| 35 | 1,601.65 | 25.06 | 1,576.59 | 1,588.98 |
| 36 | 1,601.56 | 12.58 | 1,588.98 | 0.00 |
Invoice check
Re-add an invoice line by line and compare it with the total printed on it.
| Step | Working | Result |
|---|---|---|
| Line 1 | 3 × 120.00 | 360.00 |
| Line 2 | 1 × 45.50 | 45.50 |
| Subtotal | sum of lines | 405.50 |
| Discount | 405.50 × 0% | 0.00 |
| Taxable amount | 405.50 − 0.00 | 405.50 |
| Tax | 405.50 × 10% | 40.55 |
| Total | 405.50 + 40.55 | 446.05 |
| Invoice says | entered | 446.05 |
| Difference | 446.05 − 446.05 | 0.00 ✓ matches |
Amounts are rounded half-up to 2 decimal places at each step shown, using exact decimal arithmetic rather than floating point. Results are a calculation aid, not tax or financial advice.