Investing Calculators

Small local calculators for position sizing and portfolio risk checks.

These calculators are personal tools, not investment advice. Please read the investment disclaimer before acting on anything here.

This page collects simple calculators I use or want to reuse when thinking about portfolio sizing. They are deliberately plain: the goal is to make the arithmetic visible, not to make the page feel like a trading platform.

Entry Position Size Calculator

This calculator sizes an entry position from the distance between entry price and stop loss. Set whether entry and stop prices are quoted in pence or pounds.

Pence Pounds
UK shares are usually quoted in pence.
Pence per share.
Pence per share. Must be below entry.
Pounds.
Maximum portfolio loss if stopped.
Shares to buy 2,500
Position cost £3,000
Cash at risk £500
Position size 3.00%

Formula: portfolio risk divided by risk per share. Shares are rounded down.

Privacy: calculations run in your browser only. Values are not submitted, stored by this site, or used in any server-side calculation.

DCA Contribution Calculator

This calculator estimates the effect of regular contributions over time. It is deliberately simple: fixed contribution, fixed interval, and a constant assumed annual return.

Applies to all money values.
Amount already invested.
Amount added each interval.
How often the contribution is made.
Investment period.
Nominal annual return before fees/tax.
Annual inflation used to estimate today's-money value.
Estimated end value £85,526
Total contributed £60,000
Estimated growth £25,526
Today's-money value £66,813
Contributions made 120

Assumes contributions are made at the end of each interval and returns compound at the same interval.

Privacy: calculations run in your browser only. Values are not submitted, stored by this site, or used in any server-side calculation.

P/L Scenario Calculator

This calculator shows what different exit prices would mean for a position. It is useful for checking whether an upside case, stop loss, or intermediate target matters enough at portfolio level.

Applies to position value and P/L.
Pence Main unit
Use pence for most UK-listed shares.
Pence per share.
Whole shares.
Used for portfolio impact.
Comma-separated prices in pence.
Position cost £3,000
Position size 3.00%
Best scenario P/L £3,000
Worst scenario P/L -£750
Exit P/L Trade % Portfolio %
90-£750-25.00%-0.75%
120£00.00%0.00%
180£1,50050.00%1.50%
240£3,000100.00%3.00%

Enter several exit prices to compare downside, breakeven, and upside cases.

Privacy: calculations run in your browser only. Values are not submitted, stored by this site, or used in any server-side calculation.

Stop-Loss Risk Map

This calculator compares several possible stop levels for the same entry. It shows how the same portfolio risk budget produces different share counts and position sizes as the stop moves.

Applies to portfolio value and output.
Pence Main unit
Use pence for most UK-listed shares.
Pence per share.
Used to calculate cash risk.
Maximum loss if stopped.
Comma-separated stop prices in pence.
Risk budget £500
Entry value £1.20
Stop Risk/share Shares Cost Cash risk Position
110.00p£0.105,000£6,000£5006.00%
100.00p£0.202,500£3,000£5003.00%
90.00p£0.301,666£1,999£5002.00%

Shares are rounded down for each stop level.

Privacy: calculations run in your browser only. Values are not submitted, stored by this site, or used in any server-side calculation.

Fee Drag Calculator

This calculator estimates how much an annual fee can reduce a portfolio over time. It compares the same contribution plan with and without the fee.

Applies to all money values.
Amount already invested.
Added at the end of each year.
Investment period.
Return before fees.
Percentage fee charged each year.
End value without fee £632,941
End value after fee £558,336
Fee drag £74,606
Drag as % of no-fee value 11.79%

Assumes annual growth, then annual fee, then end-of-year contribution.

Privacy: calculations run in your browser only. Values are not submitted, stored by this site, or used in any server-side calculation.

Inflation Buying-Power Calculator

This calculator shows how much future money would be needed to preserve the buying power of an amount today.

Applies to all money values.
Starting buying power.
Annual inflation rate.
Time period.
Future amount needed £12,801
Buying power if unchanged £7,812
Inflation gap £2,801

Assumes inflation compounds annually.

Privacy: calculations run in your browser only. Values are not submitted, stored by this site, or used in any server-side calculation.