Price Increase Calculator
Pounds, percentage and yearly impact
Try a £45 to £52 monthly bill · Try two successive 10% rises
Enter the old and new price for the same period. The change is new minus old; divide that difference by the old price and multiply by 100 for the percentage.
For example, £45 rising to £52 is £7 more per month. £7 ÷ £45 × 100 = 15.56%, shown as 15.6%. Twelve payments at the higher price would cost £84 more.
Enter the old price and the percentage. Multiply the old price by 1 plus the percentage divided by 100. Use a minus sign for a decrease.
A £40 bill with a 12% increase becomes £40 × 1.12 = £44.80. A 10% decrease gives £40 × 0.90 = £36. The main result shows the difference; the new price appears underneath.
Enter the price after the change and the percentage used. Divide the new price by 1 plus that percentage divided by 100.
If £110 includes a 10% increase, the original was £110 ÷ 1.10 = £100. Subtracting 10% from £110 gives £99, so it does not reverse the increase.
A change from £0 to £10 has a £10 difference, but no defined percentage increase: the formula would divide by zero. The calculator shows the pound change and explains why the percentage is unavailable.
A 100% decrease takes a price to zero. You cannot work backwards from that percentage to a unique original price. Decreases below −100% would create a negative price and are rejected. Blank or invalid fields clear the previous result instead of leaving an old answer on screen.
Weekly uses 52 payments, monthly uses 12 and annual uses one. This is a full-year comparison, not a prediction of your next bill. If a £7 monthly rise begins with six payments left this year, the remaining-year increase is £42, not £84. Part-period charges need the supplier's billing dates.
Compare like with like: convert a £480 annual charge to £40 a month before comparing it with a monthly offer. Keep setup charges separate, and check whether usage, tax or an introductory discount changed too. The tool includes only the amounts you enter and does not assess whether a price change is permitted by your contract.
For several successive rises, apply each to the previous result: two 10% rises turn £100 into £121, not £120. The bill-change guide shows how to separate a rate increase from usage and one-off charges.
Estimate only. Amounts are displayed to the nearest penny and percentages to one decimal place; calculations use unrounded values. Arithmetic and examples checked 1 September 2026. How we check calculations.